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302

Miscellaneous-Answers to Correspondents.

CHEMICAL NEWS,

Dec. 22, 1865.

ness.*

matter in
100,000 parts of

the waters.
Solid

Organic and other

volatile matter.

Amount of oxygen

required for oxidation of organic matter.

Permanent.

Temporary.

Total.

2.32

8.2 6.8

17.5 177

111 95 ILO 54

2'17

130

27.59

1 C4 073 2042 1'44

9.7 5 5 90 82

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Analyses of London Waters.-Analysis of the pelargonic ether; the other, mixtures of very variable metropolitan waters in October, 1865, by Professor Frank- composition, and apparently inferior in quality. By the land, F.R.S., of the Royal College of Chemistry :- first method, pelargonic acid is obtained by treating oil

of rue by nitric acid ; to etherise pelargonic acid, dissolve Degrees of Hard

it in concentrated alcohol, and pass into the mixture a

current of dry hydrochloric acid; the pelargonic ether rises Names of Water Companies.

to the surface as it forms. By the second method, a fatty body is treated by nitric acid, and fixed fatty acids are produced, such as adipic, pimelic, lauric, succinic, &c., and also volatile acids, which may be distilled, and of

which the chief are butyric, valerianic, capric, caproïc, Thames Water Companies.

caprylic, ænanthylic, and pelargonic. This is the mixture Chelsea

24'98 1.83 '1606

67

7.8 14'5 West Middlesex

which is to be etherised. Alcohol is sometimes scented 2530 196 1076 64 Southwark and Vauxhall

29'32
1521

with the product obtained by etherising cocinic acid, exGrand Junction 26-99 167 *0943

17.8 tracted from cocoa-nut oil; to obtain this acid, saponify Lambeth

22-76

1950 76 Other Companies.

cocoa-nut oil by potash, decompose the soap by hydroKent

38.08
0156

chloric acid, dissolve the acid thus obtained in alcohol,

177 274 New River :

*0421
156

and pass into it a current of dry hydrochloric acid ; a East London

29'14
1341

yellowish liquid will be the result; wash it with water South Essex

40*54
0140
183 | 26'5

and with alkaline water, when pure cocinic ether will The table may be read thus-100,000 lbs. of the Chelsea remain, which mix with ten times its volume of alcohol. water contained 24'98 lbs. of solid matter, of which the richness of commercial essences in pure essences may 1.83 lbs. of organic and other matters were driven off by be ascertained by distillation ; alcohol boils between 80° incineration. 1606 lbs. of oxygen were required to and 85°, and the essences remain as residue. Artificial destroy organic matter in the said quantity of Chelsea essences are not generally used in perfumery, excepting water. Of the solid matter 14'5 lbs. are carbonate of essence of mirbane; but other agreeably-scented essences lime or its equivalent ; of which 7.8 lbs. are got rid of by will very probably be some day used, carefully combined boiling, and 6'7 lbs remain.

and considerably diluted. As found in commerce, they Dr. Whitmore's Report on the quality of the water have an odour which is far from agreeable, and they, moresupplied in St. Marylebone in November, 1865:

over, have an injurious effect on the animal economy when

inhaled in sufficient quantity; they must then, if used, Total solid matter in Organic matter in de

be used sparingly.- Des Odeurs, des Parfums, et des grees or grains per grees of grains per

Cosmetiques. November. imperial gallon. imperial gallon.

Illuminating Gas from Apples.-A new use for

the marc from the cider presses has been discovered by Nov. 1864. Nov, 1865. Nov. 1864. Nov. 1865. Distilled Water

o

MM. Gouverneur, Butler, and Eichebrenner, who submit

it to dry distillation, and so obtain acetic acid, tar, and a W. Middlesex water 17:46

large amount of gas of fair illuminating power.- Resumé Grand Junc. water 17.44

1996 Pump, Princes St., Jan., 1865.

Jan., 1865

Oral, &c., par M. L'Abbé Moiyno. Oxford Street 68.96

6:56 2.88 848 Use of Ultramarine in Refined Sagar.-M. Pump, Newman St.,

Monier writes to Les Mondes that the use of indigo, reOxford Street

1'056

ferred to in the CHEMICAL News some time ago, has long As might have been expected from the late heavy rains, been given up, and ultramarine is now employed. For a the quantity of organic matter contained in the Thames boiling of 800 loaves, weighing on the average 10 kilocompanies' water during the past month has been greater grammes each, about 40 grainmes of ultramarine is suffithan in the month preceding; but, considering that this cient. This quantity, which gives about 6 centigrammes impurity must necessarily, for the most part, be vegetable, to a loaf, is enough to communicate the very slight blue the deterioration of the water is of less importance than if tint required. Ultramarine is perfectly innoxious. it were produced by animal matter. The boasted superiority of the water from Loch Katrine for drinking purposes, which is found to contain no organic matter, and

ANSWERS TO CORRESPONDENTS. not more than two or three grains of inorganic, and which All Editorial Communications are to be addressed to the EDITOR, now supplies the city of Glasgow, has to be proved by the and Advertisements and Business Communications to the PUBLISHER, at test of time. There can be no doubt that any amount the Office, , Wine Office Court, Fleet Street, London, E.C. Private of organic matter in the water we drink, however small, letters for the Editor must be so marked. especially animal, is objectionable ; but as regards the In publishing letters from our Correspondents we do not thereby mineral constituents found in the rivers and wells in and adopt the views of the writers. Our intention to give both sides of near London, of which salts of lime constitute a large question will frequently oblige us to publish opinions with which we proportion, it is a subject well worthy of consideration to determine whether such water as this does not contribute

Vol. XI. of the CHEMICAL News, containing a copicus Index, is now to supply the earthy matter which gives solidity and ready price is cd., by post, 118. od., handsomely bound in cloth, hardness to the bony structure of the human frame ; for, if price is. 6d. Subscribers may have their copies bound for 2s. 6d. if not, it seems difficult to tell from what else in our daily sent to our office, or, if accompanied by a cloth case, for 18.

Vols. 1. sustenance it is derived.

and II. are out of print. All the others are kept in stock. Vol. XII.

commenced on July 7, 1865, and will be complete in 26 pumbers. Essence of Cognac and of Wine.- This is a mix. ture of several ethers of the ethylic series, but of which

Derby.-Bunsen and Kirchoff, translated by Dr. Roscoe, but the the special odour is that of pelargonic ether. The essences

latest discoveries are not contained.

H. M.-A constant stream of ozonised air can be obtained by means may be prepared in two ways: the first gives nearly pure of the apparatus described at pago 1?, vol. x., of the CHEMICAL News. * The degree of hardness hitherto employed by chemists is that experiments.

Clericus. - We do not remember to have met with any account of the first proposed by Dr. T. Clark-viz., one grain of carbonate of lime, or its equivalent, in one imperial gallon of water, or one part in 70,000. pints; red ink, cochineal, oxalic acid, and gum arabic.

Copying Ink.-Sugar candy, an ounce; rich black ink, one and a hall The degrees of hardness used in the above table are readily converted into Clark's degrees by multiplying by 7, and then moving the decimal phosphorus paste; or of nitre, oxysu phuret of antimony, and flour,

Vesuvians are made of nitro and "charcoal tipped with the usual point one place to the left.

tipped as before.

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Career car istisms,} On the Manufacture of Commercial Carbonate of Ammonia.

303

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SCIENTIFIC AND ANALYTICAL

a patent for obtaining ammonia from peat, and Mr.

Rees Reece in 1849 also had a patent very much like CHEMISTRY.

Mr. Hills'. The first part of the patent is for an inven

tion for causing peat to be burned in a furnace by the Action of Carbonic Oxide on Sodium-Ethyl, aid of a blast, so as to obtain inflammable gases, tarry by J. ALFRED WANKLYN.

and other products. The tarry products may be emThe action of carbonic oxide on sodium-ethyl is of a very ployed to obtain paraffine and

oils for lubricating maremarkable character. Carbonic oxide drives out sodium chinery, &c., and the other products may be made and gives a compound of carbonic oxide with ethyl. The available for evolving ammonia, wood spirit, and other following equation represents the change :

matters by any of the existing processes. On July 27, CO + 2NaC,H, Na, + CO(CH3).

1849, a statement was made in the House of Commons The product CO(CH3), is the ketone, ethyl-propionyl.

to the effect that 100 tons of peat would produce 2602 A detailed account of the research will be published in pounds of carbonate of ammonia. the Journal of the Chemical Society.

In 1841 Mr. Laming took out a patent for manu

facturing carbonate of ammonia by mixing its separate London Institution, December 27, 1865.

acid and alkaline constituent, instead of by the decom

position of ammoniacal salt. One of the processes used TECHNICAL CHEMISTRY.

is to cause ammonia and carbonic acid

gas obtained separately from any convenient sources to traverse a

succession of leaden chambers maintained at as cool a On the Manufacture of Commercial Carbonate of temperature as may be conveniently practicable, and so

Ammonia, by J. Carter Bell, F.C.S., Associate of continued as to favour the admixture of the dissimilar the Royal School of Mines.

gases. In this process it is not essential that the two This salt must have been known even to the alchemists, gases be present in their combining proportions; it is as it forms one of the chief constituents of putrid preferable that the carbonic acid be in greater abundance urine, but there seems to be no evidence that it was than will combine with the ammonia which is present. manufactured previously to this century; indeed, one Sometimes a stratum of water, or of water impregnated would hardly think that they knew the difference with ammonia, is placed in one or more of the leaden between ammonia and its carbonate. The real differ- chambers. Carbonic acid and ammonia in the form of gas ence was first pointed out by Dr. Black, of Edinburgh. are then introduced; in which case, it is stated, a larger

Carbonate of ammonia is formed by the putrefaction proportion of carbonic acid gas is found in the resultof animal substances, and by the destructive distillation ing salt, or saline solution, than when only the hygroof animal matter.

metric moisture of the aëriform fluid is present. Mr. In the destructive distillation of bones, carbonate of Laming also converts the hydrosulphate of ammonia ammonia is produced, and also water with the oil called contained in gas liquors into carbonate of ammonia by “ Dippel's oil," with some incondensible gases. The con- the following process :- A mixture of deutoxide of densed liquors from the carbonisation of the bones are copper and charcoal, or other form of carbon in fine separated into two distinct states-the oily and the powder, in the proportion of twelve parts by weight of aqueous products—the latter containing the carbonate the former to one of the latter, is introduced into a retort of ammonia ; the salt can be separated by sublimation. made red hot and furnished with an eduction pipe which

Many processes have been tried for the manufacture of passes through cold water, and finally enters into the this compound. Iam informed by Mr. John Hogarth (who gas liquor. The formation of carbonic acid gas soon has been engaged in this chemical operation for forty takes place by the union of the carbon with the oxygen years) that in the year 1825 a Mr. Holmes manufactured of the metal, and this gas combining with the base of this sult in the old Haymarket, Liverpool; it was made the hydrosulphate of ammonia converts it into carfrom stale urine, and the resulting blocks were very bonate, with liberation of sulphide of hydrogen. When small, weighing about six pounds. At the present the carbonic acid ceases to come away, nearly all the time the weight of a block is about two hundredweight. carbon will have disappeared from the retort, and the

On March 11, 1844, Dr. Wilton Turner took out a patent oxide of copper reduced to the metallic state. The for obtaining salts of ammonia from guano, The guano charge is then drawn, and left to cool while a second is subjected to destructive distillation in close vessels at charge of sirailar materials is being worked off; during a low red heat during the greater part of the operation, which time the copper reabsorbs oxygen from the air, but the temperature is increased towards the end. Thé and becomes again deutoxide of copper, which may be products of distillation are collected in a series of used anew with fresh carbon. Woulfe's bottles, by means of which the gases evolved Messrs. Crane and Tullien, in their patent of January 8, during the operation may be made to pass two or three 1848, describe a method of manufacturing ammonia in times through water before escaping into the air. The the state of carbonate, hydrocyanate, or free ammonia products consist of carbonate of ammonia, hydrocyanic by passing any of the oxygen compounds of nitrogen, acid, and carburetted hydrogen ; the first and second are together with any compound of hydrogen and carbon, rapidly absorbed by the water, with the formation of a or any mixture of hydrogen with a compound of carbon, strong solution of hydrocyanate and carbonate of through a tube or pipe containing any catalytic or con. ammonia.

tact substance. The substance which is preferred is In 1849 Mr. Hills took out a patent for obtaining car- platinum in the state of sponge, or asbestos coated with bonate of ammonia from guano, To effect this the platinum. This is to be placed in a tube and heated to guano is first mixed with charcoal or powdered coke; about 600° F., so as to reduce the temperature of the the mixture is then heated, and the carbonate obtained product, and at the same time prevent the deposition by sublimation. Peat has been experimented on for the of carbonate of ammonia, which passes onwards to a production of this salt ; whether it will be an econo- vessel of the description well known and employed for mical process remains to be proved. Mr. Hills took out the purpose of condensing carbonate of ammonia. The

VOL. XII. No. 317.--DECEMBER 29, 1865.

304

On the Manufacture of Commercial Carbonate of Ammonia. (Cheeseca, News

condenser for this purpose must be furnished with a leading to the balloons are well cleaned out, as they are safety pipe, to allow the escape of uncondensed matter, very liable to become stopped up. The used-up charge, and made to dip into a solution of any substance capable which consists principally of chloride of calcium, is of combining with hydrocyanic acid or ammonia. drawn out into an iron barrow and wheeled away to some

Carbonate of ammonia is manufactured at the present waste ground ; the new charge (which is generally turo time from a mixture of sulphate or chloride of ammo- of chalk to one of the salt) and which has been carefully nium and common chall, heated in retorts and sublimed. weighed and well mixed, is thrown quickly into the The decomposition of the chloride of ammonium may be retort, the door is luted on, and then the retort is left represented thus :

for trenty-four hours, the contents receiving an occa(IIN, Cl) +3(CaO,CO.,)=3CaCl + 2HN0,3CO, +

sional stir. II N +TÍO.

When the retorts hare been worked for about fourteen In the manufacture of ammonia alum, the ammonia ise days, the balloons are opened, and the impure carbonate derived from gas liquor ; the liquor is heated, and nearly is found as a thick crust lining all the sides; it is deall the rolatile ammonia driven off. The residue is taken posited in different coloured layers, according to the imout of the boilers and used for the manufacture of car- purity of the carbonate. The chief impurities will be bonate of ammonia. It is treated with a little acid till carbonate of lime and chloride of calcium, which are it is neutral, then evaporated by means of heat in large carried over mechanically; the salt is well scraped down hemispherical iron pans set in brickwork. When it has from the sides, and the balloon prepared for another arrived at the crystallising point, it is allowed to cool, fourteen days' operation. These balloons have to be of and crystals are then deposited; or the hot liquor may considerable size, or there would be much waste from the be run into other coolers for crystallisation. The mother salt being carried off by the steam; in each balloon is a liquor is syphoned off, and then the inside of the pan is small test-hole, closed with a plug of wood, this is for seen studded with intense black crystals, of the prismatic telling how the sublimation is going on. The impure form when sulphuric acid has been used for the neutrali-carbonate is all collected and taken to the resublimation sation, and cubical with hydrochloric acid. The crystals pans. The salt is put into iron tanks about sixteen feet are now shovelled out of the pan, and washed with the long and two and a-half deep; they are wider at the mother liquor. They are then re-dissolved, the liquor bottom than at the top, being two feet seven inches run into coolers, and re-crystallised. In the re-dissolving at bottom and two feet at top. These tanks are closed a great deal of sediment is deposited, consisting chiefly with two plates of iron with four holes in each, about of the matter mechanically locked up in the crystals. The one foot in diameter and one foot apart from each other. crystals when dry are of a dirty white colour; they are Over every hole is placed a conical leaden vessel with a now ready for the next operation of converting them fat top. These ressels are formed of a sheet of lead, and into carbonate of ammonia. For this purpose cast-iron the two ends are kept together by means of staples and retorts, the shape of an elongated muffle, are used. The wedges; a circular piece of lead is luted on the top of neck of the retort is round, and closed with an iron door, these receivers ; the height of them is about two feet. kept in its place by means of a screw. The retorts are

The tanks are set in brickwork, with a fireplace about seven feet long and one and a-half deep. Three at each end... They are charged every fortnight ; a are set in brickwork in the form of a triangle, and heated certain quantity of water is first put in, then the imby one fire. They communicate by means of iron pipes Their respective holes, and a small fire made at each end

The receivers are all luted on over with a leaden chamber which is technically called a balloon. It is about six feet high, eight long, and two of the tank. Great care is required in regulating the and a half wide. These balloons are supported upon temperature, because the heat must not be too high, as scaffolding so as to be on a line with the retorts, and the salt sublimes from 120° to 130° Fahrenheit. In the are kept in their places by means of iron bands. At the end receiver is a small hole closed by a plug; on taking bottom of each balloon is a small pipe, which is always this out it can be seen whether the temperature is too kept open to allow for the escape of steam, and water high ; if it is, the fires have to be damped. A thermohighly charged with carbonate of ammonia. There is a meter is generally used, but some people prefer to trust constant dropping from this pipe, which is collected in a to their own judgment. Instead of the tank and fires pail, and re-sublimed. If this pipe were not there, the separate pots may be used, each one being surmounted pressure inside the balloon might cause it to be blown by a leaden cap; these pots are either set in brickwork off the scaffolding: Great attention has to be paid to and heated by the flue of the retort furnace, or they may the heating of the retorts. If they were heated too be set in a water bath. At the end of fourteen days the strongly, most disastrous results might occur.

leaden receivers are lined with a thick crust of carThe retorts are charged once every twenty-four bonate; they are taken down, and the lead stripped off; hours with a mixture of carbonate of lime and am the outside of the block is rather dirty, it is well scraped, moniacal salt; the chalk is well dried on an iron and then broken into pieces, packed in jars, and sent to plate which is set over the flue, so that the waste the market. The leaden receivers are well washed and heat of the fires economically dessicates it. All the reshaped. A small quantity of the residuary liquor is retorts are not charged at the same time, for often there taken out of the tanks, but the chief part is left in, a are five and six sets; if they were, the labour would fresh charge of carbonate is added, the receivers are be too great, and a greater number of men would be re- luted on, and the operation goes on the same as before, quired; but to do away with that difficulty one retort in The greatest use which is made of this salt is by cach set is charged at the same hour every day; the first bakers and confectioners; it is largely, employed in charging takes place at seren, the second at eleven, and medicine and in the manufacture of smelling salts. the third at three, and by that time the whole of the retorts have been charged. The contents are frequently Royal Institution of Great Britain.—The folstirred up with long iron rods (which are pushed through lowing are the lectures for the ensuing week:–Tuesday, holes made in the door of the retorts) to assist the de- Jan. 2, Thursday, Jan. 4., and Saturday, Jan. 6, 3 o'clock, somposition. Before a new charge is put in, the pipes Professor Tyndall, “ On Sound” (juvenile lectures).

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PROCEEDINGS OF SOCIETIES.

for the twofold purpose of hardening the gold and securing its perfect adhesion to the brass, and fine lines or divisions

could then be engraved upon the face of the bar in such a CHEMICAL SOCIETY.

manner as to remove the film of gold in those parts. By Thursday, December 21.

the action of the air upon the exposed portions of brass, Professor W. A. MILLER, M.D., F.R.S., President,

distinctly marked lines would soon be formed of a black in the Chair.

or greenish-bronze colour upon the bright gold ground.

A bar, very attractive and ornamental in its character, The minutes of the previous meeting were read and the would thus be produced, and one which the author conseveral donations to the Society's library were acknow- sidered to be admirably adapted for use as a mural ledged in the usual manner. Mr. William J. Barnes was standard, and by placing the yard and metre in apposiformally admitted a Fellow, and the following gentlemen tion, would be likely to find favour and inform the minds were duly elected by ballot-viz., John Percy, M.D., of the British public. Several of these could be prepared F.R.S., lecturer on metallurgy, Royal School of Mines ; and set up on the outside walls of public buildings both in Mr. Ernest T. Chapman, 25, Somerset Street, London ; the metropolis and in the provinces, if the cost of from Mr. Charles N. Ellis, Bow Common; and Mr. Thomas three to four pounds each would not be judged excessive. Ward, Mechanics' Institution, Bolton. The names of the Mr. Yates then referred to the possibility of reducing the candidates read for the first time were, -Mr. Edward cost by the substitution of a coating of platinum, or of an Purser, jun., 116, Fenchurch Street; Mr. William Thorpe, alloy of platinum and iridium, for the gold; and proceeded 13, York Terrace, Kingsland Road; Mr. Arthur E. Davies, to enumerate other suggestions relative to the employment Surgeons' Hall, Edinburgh; and Mr. Franklin Epps, of the best kind of aluminium bronze (60 parts copper and Great Russell Street ; and for the second time the names

40 of aluminium); speculum metal, improved by the addiof the following,-Mr. Thomas B. Redwood, 19, Montague tion of a little arsenic; and lastly, for in-door applications, Street, Russell Square ; Mr. John Conroy, Christ Church, of steel, which had the sanction of the Rev. R. SheepOxford ; Mr. James Speir, Newcastle-on-Tyne; and Mr. shanks, although it was well known to be liable to rust, Robert Henry Smith, Rodney Street, Penton ville.

The author stated that he noticed rust upon the steel The PRESIDENT said he was glad to notice among the standard last referred to, even whilst it was on view at visitors the presence of several gentlemen who had given the Paris Exhibition of 1855, and he believed its condition attention to the subject of Mr. Yates' paper ; letters of could now be ascertained by a visit to the Conservatoire invitation had likewise been addressed to the Astronomer des Arts et des Metiers. The author concluded by referring Royal and other eminent authorities, who were, however, to mural standards already open to public inspection on unable to attend.

the outside walls the Royal Observatory, at Greenwich, A communication entitled, On the Best Material for and of Messrs. De la Rue's manufactory, in Bunhill Row; Mural Standards of Length," was read by Mr. JAMES by exhibiting some accurate metre scales prepared by Mr. Yates, M.A., F.R.S. The author referred to a previous James Gargory, 41, Bull Street, Birmingham, and by essay on this subject which he presented to the British Messrs. Elliott Brothers, of the Strand, London, besides Association for the Advancement of Science, and had the lithographic representations of the same ; and invited dishonour of reading at the Birmingham meeting in Sep. cussion upon the sereral points raised in his paper, protember last. Uis communication was followed by others mising for himself and colleagues to submit a statement stating the advantages of the metric system, and gave rise embodying the chemists' decision to the ruling authorities to an animated discussion, in which Dr. Williamson and of the British Association, other eminent chemists took part ; and the result was that The long and interesting discussion which followed the the Association appointed a committee for the purpose of reading of Mr. Yates's paper will be reported next week. promoting the extensive use of the metric system | Before adjourning the meeting, the PRESIDENT mored a in scientific documents, the teaching of the system vote of thanks to the author, and announced that on the in schools and colleges, and for the general informa- next occasion, January 18th, Dr. J. H. Gladstone would tion of the people. The author's previous remarks read a paper, On Pyrophosphotriamic Acid," and that on on mural standards were arranged under the follow- 1st February Dr. Gilbert would address the Society upon ing heads :- The material; the form and dimensions; an agricultural subject. the description by means of letters, figures, and other marks; the distribution and exposure to public view; the use in education; the aids to be affo:ded by

PHARMACEUTICAL MEETING. the British Association. To the first of these heads--viz.,

Wednesday Evening, December 6. the material--the author proposed on the present occasion to limit himself, and he wished now to have the opinion

(Continued from page 299.) of the Fellows of the Chemical Society upon this point. DR. ATTFIELD read a paper entitled Observations and He had already offered (at Birmingham) a suggestion that Experiments on the Physics of Filtration.Dr. Attfield's Baily's metal be employed, but since that time doubts had paper was of great length, and our space allows us to give been expressed in regard to the permanence of this metal but a very short abstract. He began by thus defining the under the usual conditions of atmospheric exposure. nature of filtration :--" The nature of the operation of filBaily's alloy consisted of copper sixteen parts, tin two tration, as usually conducted, is so simple that but little and 'a-half, and zinc one part, and the use of it had been has been or need be published concerning it. The variety recommended in the “ Act for Legalising and Preserving of circumstances under which filtration is conducted, as the Restored Standards of Weights and Measures,” 18th well in social as in commercial life, has given rise to many and 19th Victoria, cap. 72, and actually adopted by the contrivances for effecting the operation ; filtering materials Royal Commissioners in 1843 under the supposition that are numerous, the forms of the vessels designed to hold it could not rust or form a loosely adherent oxide. An the materials scarcely less numerous, and the arrangements adverse opinion having lately been expressed, the author to facilitate and perpetuate filtration many and ingenious ; proceeded to criticise the respective advantages of a variety but the nature of the operation, as distinguished from the of other metals, alloys, and compound bars, which seemed operation itself, is the same, or nearly so, under all ordito be capable of employment for these purposes, and ad- nary circumstances. Indeed, its nature is identical with vocated-if no scientific reasons should appear to the con- that of some operations which, conventionally, are quite trary-the use of ordinary brass covered with a thin coat- distinct from filtration, and which are always spoken of by ing of gold. The metals should be drawn out together, other names. In the process termed sifting we have the

306

Pharmaceutical Meeting.

CUEMICAL News,

Dec. 29, 1865.

same action occurring as in filtration ; it might, in fact, be though not apparently, a flow proportionate to the square called • dry filtration.' * In the netting of fish we also have root of the amount of force which produces it. For in. the same action. Again, the operation of straining 'even stance, a filter is giving a certain number of drops per still more closely resembles that of filtration. The nature, minute, under a certain amount of force; double the then, of the operations conducted with filters, strainers, amount of force, and we get nearly double the number of sieves, or nets is identical ; the operations themselves quite drops : in the first case, nearly all the force is expended distinct, and, rery properly, called by different names. in producing static pressure within the instrument, the What I wish to speak of now is not the operations them- residue being expended in producing the flow; in the selves, but their nature—that is, the laws which regu- second case, also, nearly all the force is expended in prolate their action, especially in respect to filters." After ducing static pressure within the instrnment, but not quite noticing the resistance offered by various filtering media, twice as much as in the first case : thus, probably, the he dwelt at some length on the different aids to filtration residue of power is four times greater than in the first

- viz., (a) hand pressure, (b) lever or screw pressure, (c) case, and hence we get a double How. And so on, until, hydraulic pressure, (d) atmospheric pressure, (e) hydrody- with a free orifice, there is no static pressure at all within namic force, or to a combination of these forms of pressure. the instrument, when we get a rate of flow which is appaUnder the fifth head, filtration aided by hydrodynamic force, rently as well as actually dynamic. It is for these conthe author described the filter invented by Mr. Schacht, in siderations chiefly that I think we should regard filtration which the pressure is produced by the influenceof a column in a dynamic aspect. A less strong, though more obvious of water below the filtering medium. With this instrument reason, is that useful filtration, that is, rapidity of flowDr. Attfield has made numerous experiments, the results is in proportion to the extent to which dynamic laws of which are of no immediate practical interest. We obtain in filters. Secondly, we have been told that presappend the author's summary, which will give our readers sure filters have not hitherto proved of the service in an idea of the scope and results of Dr. Attfield's experi- Pharmacy that was expected of them; that where they ments :-—"The practical applications of the truths we have are most needed-namely, for the separation of solid been considering are for the most part obvious, and already matter in a very minute state of division or in a flocculent well known to all. But of what new value are they? as condition, there they fail, and that a turbid instead of a follows :-Firstly, these observations and experiments give clear and bright filtered liquid results. Now, so long us, I think, clearer, more correct views of the nature of as we consider pressure-filters to be static instruments, the operation of filtration than most of us had before. this result must be inexplicable. But once realise We should, I think, regard filtration under any and all their dynamic character, and the explanation of the circumstances from a hydrodynamic point of view. We fact would to be this, -- a flock or particle should regard it as the flow of a liquid from an orifice in of solid matter finds itself at the mouth of a pore of a the vessel containing the liquid, the flow being interfered filter; if that particle were the object of static laws only with or resisted to a greater or less degree by a porous (aërostatic or hydrostatic), there it would remain, resting, fabric, termed a filtering medium. The rate of flow we so to speak, on the edges of the pore, and there it would should regard as normally following that described in the remain, we will suppose, if the pore were the pore of a theorem of Torricelli-namely, in proportion to the square common filter in a common funnel, the pressure that is root of the distance from the orifice of outflow to the above the particle being in this case only slightly greater surface of the filtering liquid ; or, as the law may perhaps than that below the particle; but now greatly increase be stated for our purpose, 'the rate of flow is proportionate the pressure on that particle from above, either directly by to the square root of the power,' whether that power be adding pressure, or indirectly by taking pressure from derived from gravitation, muscular or mechanical force, or below, then the particle is at once shot through the pore, the elasticity of compressed air or steam. As the flow it being compressed if it be a flock, or it itself enlarging becomes slower and slower, the manifestation of this the fibrous interior of the pore, if the particle being indynamic law becomes less and less evident, and he compressible, and if the pore be in paper, cotton, existence of a static law in the instrument more and wool, &c. In other words, the force which increases the more evident, until, when the flow ceases altogether, a gravitating motion of fluid particles through the pores of static pressure only exists within the apparatus; hydro- å filtering medium, increases the gravitating tendency of static in the common conical and other simple filters, the any solid particles which may be resting within or on ihe filter bag pressed in the various ways, and the filter in edges of those pores. This' explanation (and the being which there is a column of liquid above the medium; able to give explanations of facis is a matter of practical aërostatic where the air is removed from below a medium value) follows, I think, from the consideration of our or additional air, &c., forced on the filtering mixture from subject. In Mr. Schacht's pressure-filter, this stated above, or where there is a column of liquid maintained objection to the old pressure-filters may possibly not obtain, below the medium. As a filtering medium always presents because the pressure can be increased so gradually that some resistance, dynamic laws can never apparently ex- the consolidation of the particles of solid matter, which clusively obtain in a filtering apparatus, though they are constantly increasing the resistance of the filtering nearly do so in the filtration of water for drinking pur- medium, goes on pari passu with the pressure itself; in poses. So also, as that resistance can never be complete, other words, the closeness of the filtering medium in his filtration can never be a static operation, nor can static instrument increases regularly with the pressure instead of law exclusively obtain in a filtering apparatus, until the spasmodically, as in other older instruments. Whether this latter ceases to be a filter, though they nearly do so when be so or not, can only be determined by experience in the the filtered liquid is escaping drop by drop, as may gene- use of his filter. Thirdly, apply hand pressure, lever, or rally be seen in an analyst's filter. Though, however, a screw pressure, and hydraulic pressure, directly to as filtering apparatus can never be the exclusive seat of either small a portion of the surface of a filter-bag as possible. dynamic or of static laws, it is quite possible that the flow Fourthly, if, in filtration, pharmaceutists, engineers, and from the apparatus is governed purely by dynamic laws. others desire to have the full benefit which ihe use of a The rate of flow does not appear to be a pure dynamic rate. long column of liquid below their filter gives them, that probably because we can only compare it with the total column must be perfectly continuous,- there must be no amount of force applied. But a portion of that force is break in it caused by the introduction of air from without expanded in producing static pressure within the instru- the instrument, or by the accumulation of air coming out ment; the residue, if we could estimate it, would pro- of solution in the water, as we all know it will do when bably show that the flow from the filter is actually, atmcspheric pressure is removed. The practical means of

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Similarly, Altration " might be called “wet sisting." getting rid of such accumulations I have already described

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