The muddy solution is run into a tank from which it is pumped to a filter-press where the sediment and gypsum is separated, the clear phosphoric acid solution being run into evaporating pans. The residue in the filter-press is then washed with water till the washings have a con. centration of o 25° B. or less. These washings are used to dilute the sulphuric acid employed in the process. Before the phosphoric acid produced can be used for making double acid phosphate it must be concentrated. This is usually done by evaporating in iron pans lined with stone or some acid resisting material. After concentrating to about 56° or 58° B., it is run into lined-lead tanks from which it is drawn or pumped as required. The mixing of this phosphoric acid with phosphate rock and all subsequent operations are practically the same as those employed in making ordinary acid phosphate, but the final product often has to be artificially dried since it contains but a small percentage of gypsum. Ordinary acid phosphate, as we have seen, is largely a mixture of soluble lime phosphate and gypsum, the latter having been formed from calcium sulphate by extracting the excess of water from the mass. Double acid phosphate, however, consists chiefly of soluble lime phosphate with but little calcium sulphate to act as a dehydrating agent, and therefore requires artificial heating to drive off the excess of water. (To be cont nued).

On account of the great demand for the electrolytic fluid the Depot had to be enlarged, and an additional new plant, with electric motor for stirring, and switchboard, &c., was installed at the beginning of 1910, and, with alterations to the first plant, cost in round figures £500. Owing to the extension of the Electricity Works the whole structure and installation had to be dismantled, and was re-erected on the opposite of the Violet Road.

During the working of the apparatus, a period of nine years, many improvements for the municipal success of the installation have been made, the expenses of which come under the heading of "Sundries and Petty Expenses" in the table of the average expenditure for the three years ended March 31, 1914.

Among the improvements a very important one has been introduced for the reception of the fluid from the electrolysers. Instead of the glass receptacles, which are

Report to the Public Health and Housing Committee, Metropolitan Borough of Poplar, June 1, 1915.

A double cell has been constructed of slate, in such a form that the "creeping" of the current (which comes direct from the Council's mains) from one cell to another is prevented. This is a most important item. All slate contains metal, and the current in "creeping" from the electrodes in one cell to the electrodes in the other cell causes erosion to take place, and sooner or later a "dead short" happens and a new double cell is required, which is an expense.

The present cells are earthenware and replaced the original slate ones, and were made by a firm of potters in the Borough at the special request of the Medical Officer of Health and under his direction and supervision, potters outside the Borough having refused to make them, as they stated the baking would be a failure. However, the tanks or cells were made, and, as stated above, are the present ones, having been in use for some years. Electricity, on account of moisture, will even creep with an earthenware cell and efficiency will be lost, and if the partition of the earthenware cell or tank is not properly glazed it will in course of time become destroyed by the electrical current (240 volts and 20 ampères) acting upon the fluid, which soaks into the unglazed earthenware. Earthenware cells take a long time to make (possibly four months), and one is never certain that in the firing of earthenware there will not be defects in the articles when they are taken out of the kilns. A slate double cell can be made in a few days, is cheap, and as now constructed will not permit the current to "creep" and erosion to take place, whereby we have cheapness, safety, and greater efficiency. The current being taken direct from the Council's mains saves the expense of a "converter," with its consumption of current and necessary skilled attention.

Since the installation of the plant 381,794 gallons of fluid have been manufactured, at a cost for electricity of £401 19s. Id. and materials of £345 9s. 11d. (under d. per gallon).

The Public Health Department is not only furnished with the electrolytic disinfectant, and the various instituWorks Department as required), but the institutions of tions of the Council (the public baths, &c., and the the Managers of the Sick Asylum and of the Board of Guardians (within and without the borough) are supplied with an unlimited quantity free; also some of the London County Council public elementary schools.

Report of a Committee of the Royal Sanitary Institute, re the Purification of the Water of Swimming Baths, November, 1912.

"The Committee also investigated the treatment of bath water by electrolytic fluid, which is in use at the Poplar Baths, and was very much impressed by the good results obtained. By the addition of hypochlorite of magnesia solution to the pond water, in amount sufficient to give one part of free chlorine to every one or two million parts of water, not only is the water sterilised, or deprived of all organised living molecules, but it is kept sweet and free from odour, and there is no tendency in the water to the deposition of slimy sediments on the floor of the pond. A certain amount of slimy matter collects on the walls of the pond at the line where the surface of the water is in continual movement from the undulatory motions induced by the movements of the bathers, but this is readily removed with a swab by an attendant. . . . It should be said that the electrolytic fluid in the Poplar Baths is not used with idea of rendering unnecessary periodic changes of the pond water, but to keep the water in the pond fresh and free from harmful organisms all the time it is in use. The class of persons who use the swimming ponds in Poplar is always likely to contain uncleanly or infected individuals, and it is to guard against danger from the latter that the fluid finds its chief application."

Respecting the stability of the fluid as manufactured in Poplar, a long article appeared in the Lancet of January 18,

CHEMICAL NEWS, July 2, 1915

}

1908, under the heading of "Electrically Produced Fluids containing Hypochlorites: their manufacture, and the rationale and chemistry of the process for securing stability." It is well known that the fluid as made in Poplar is rendered stable for an almost indefinite period, and is suitable either for municipal or for commercial purposes. The rendering of quantities of hypochlorite of magnesia electrolytic fluid stable for municipal purposes was the difficulty which had to be overcome with the plant erected in Poplar, because no plant was in existence prior to the Poplar plant where this had been done on a large scale. Upon the visit to Rolleville, France, in the year 1905, after the first report of the Medical Officer of Health to the Council, the then Chairmen of the Public Health, Electricity, and Works Committees-Messrs. A. G. Smith, J. Bussey, and F. Thorne respectively-and the Electrical Engineer and the Medical Officer of Health, a small plant for making a medical solution was exhibited, but this plant was indeed very different to the one supplied to the Poplar Borough Council, and could not possibly have made fluid in quantities sufficient for municipal purposes. This small plant at the time of visit was stated to have broken down, being not at work.

The success which has attended the working of the plant has been largely due to the loyal support and mechanical ability of the chief disinfector, W. D. Quested, and also to the interest and care displayed by C. Hagon, who has the immediate charge of the apparatus during the manufacture of the fluid. J. Harber, the labourer, has also faid great attention to the work, and can be entrusted with the management of the machines when necessary.

The work of making electrolytic disinfectant as carried out in Poplar has been appreciated. Plants have been supplied to Guernsey, Gateshead, Finland, Buenos Ayres, and Rangoon. At Portsmouth a plant has been installed for manufacturing the fluid direct from sea-water, and rendering it stable by the method adopted in Poplar. Recently the Finchley Council placed an order for an installation.

Shortly after the commencement of the war the question of obtaining the necessary materials for the manufacturing of the electrolytic disinfectant was considered, as chloride of magnesium had been obtained in the past from Germany. The normal price is £4 5s. per ton delivered free at the depot, but the price went up to £14, the present price ranging from £11 to £14 per ton. Three tons were secured at £4 8s. per ton, one ton at £6, and seven tons at £7 58. per ton.

With regard to other materials, ten hundredweight of caustic soda was procured at an increase of id. per lb., to be delivered in quantities of 192 lbs. as required. Ten tons of salt, the usual price of which is £1 148. per ton, were obtained at an increased cost of 2s. 6d. per ton for

cartage.

It is estimated that the present stock of the above materials—with the exception of caustic soda, which can be obtained as required-will last twelve or fifteen

months.

WELSH NOTES.

(By Our Special_Correspondent).

IT is a significant indication of the way in which trade generally is being maintained at the Swansea Docks that the total tonnage for last week only just fell short of the total for the corresponding period of last year, which was an exceptional one. Imports were quiet, but the coal and patent fuel exports displayed considerable activity. Noticeable among the imports was a 4460 tons cargo of iron pyrites from Spain. Shipments of patent fuel amounted to 15,791 tons, tinplates and general goods 14,325 tons. Boxes of tinplates received from works aggregated 77,433, whilst 226,850 represented the stocks in dock warehouses

and vans. Shipments amounted to 163,439 boxes. Minor imports included 514 tons scrap iron and steel, 335 tons pitch, and 400 nickel matte.

As has been the case during the past few weeks, great activity was everywhere observed in the Swansea Valley during the week, the chief complaint being a lack of labour. At the Landore Blast Furnaces the men were engaged for very long periods in order to cope with the work, and it is safe to say that not for many months has the steel trade of the Swansea Valley experienced such great pressure. The copper trade was satisfactory, all refineries being fully engaged, and a high yield of copper plates followed. A good demand prevailed for all classes of material at the various spelter works. Tinplates brightened up very considerably, the Duffryn, Forest, Beaufort, and Worcester works being fairly well maintained, although occasional stoppages took place at the Upper Forest Works. The bar mills and sheet trade, however, were still unaltered. The safety fuse works and lead-pipe works were very brisk indeed, and all departments of the Mond Nickel Works were fully employed. The Mannesmann Tube Works were having a good call for material. As usual, however, the sulphuric acid factories were very slack, there being very little demand for vitriol. Metal extraction works were kept going fairly well.

Port Talbot Dock trade was satisfactory, although a small decrease in comparison with the corresponding period last year was registered. Patent fuel exports totalled 3,304 tons, whilst chief among the imports were 1300 tons pitch and 1608 tons pig-iron. Tinplates as usual were very dull, but the Morfa Copper Works were running at high pressure, a great deal of Government work being in hand. At the Dowlais Works all departments were very busy during the week. The Goat Mill was engaged on heavy steel rails, steel sleepers, and billets, and some tin-bar, sole-plates, and steel bars were also run there. The Big Mill turned out a fine crop of short steel bars, rails, and curves, and a quantity of fish-plates. The Blast, Bessemer, and Siemens furnaces were also busy. The finishing departments were well employed, and the dispatching of the finished material was done with smartness.

PROCEEDINGS OF SOCIETIES.

ROYAL SOCIETY.
Ordinary Meeting, June 17, 1915.

Sir WILLIAM CROOKES, O.M., President, in the Chair.

PAPERS were read as follows:

-:

"Soil Protozoa and Soil Bacteria." By E. J. RUSSELL. In view of the claim recently made by Goodey that soil protozoa cannot function as a factor limiting the numbers of bacteria in soils, the author has brought together the evidence on which this view is based.

It has been shown in numerous experiments that the numbers of bacteria in normal soils are relatively low, but they can be raised by any treatment that kills trophic forms and not spores. Starting, in the first instance, to find the properties of the factor which keeps down the bacterial numbers, and without framing any hypothesis as to its nature, these were found to be: (a) active, and not a lack of some essential; (b) not bacterial; (c) extinguished by heat or poisons, and after extinction does not reappear; (d) can be reintroduced by adding a little untreated soil; (e) is favoured by conditions favourable to trophic life in the soil.

These properties indicate that the factor is biological. Search was therefore made for organisms fulfilling these conditions, and numbers of protozoa were found. Definite evidence has been obtained that trophic forms occur as normal inhabitants of the soil, and the estimates of num

bers so far available show that they are considerable. There is the closest possible relationship between the extinction of the protozoa and the extinction of the limiting factor, and also between the re establishment of the protozoan fauna and the setting up of the limiting factor after reinfection with small quantities of soil.

Hitherto the reinfection with mass cultures of selected protozoa has not had the effect of reducing bacterial numbers, but this is attributed in part to the difficulty of obtaining a suitable control, and in part to the fact that the fauna developing in culture infusions (from which the organisms were selected) differs from the trophic fauna, the forms predominating in the one not necessarily figuring largely in the other. Until more is known of the lifehistory of the protozoa of the soil, it is unsafe to attach too great importance to failure of reinfection experiments made with mass cultures of forms prominent in hayinfusion cultures from the soil.

"The Enhanced Series of Lines in Spectra of the Alkaline Earths." By Prof. W. M. HICKS, F.R.S.

A discussion of the enhanced series of the alkaline

earths is carried out in order to determine their relation to the oun.

For this purpose the results given for Mg, Ca, Sr, by Fowler in his recent Bakerian Lecture are used, and, in addition, the corresponding series in Ba and Ra are considered. It is found that the quantity A', giving the doublet separations, is given with great accuracy in terms of the oun, as follows:

Mg, 568; Ca, 688; Sr, 588; Ba, 5638; Ra, 608, where & is four times the corresponding oun for the element.

The satellite separations are also found as functions of the same quantity. Further it is shown that these series strongly support the general relations given in a former communication that the first p-sequence depends on a multiple of the atomic volume, and that the diffuse sequence is such that the denominators of the first lines, when the wave number is expressed in the formA-N/(den), are themselves multiples of A' or of the oun. "Certain Linear Differential Equations of Astronomical Interest." By Prof. H. F. BAKER, F.R.S.

"On the Partial Correlation-Ratio." PEARSON, F.R.S.

Prof. KARL

"Effect of Temperature on the Hissing of Water when Flowing through a Constricted Tube." By S. SKINNER and F. ENTWISTLE.

The experiments deal with the temperature coefficient of the effect described by Osborne Reynolds before the British Association at Oxford, 1894. It is shown that the velocity at which hissing just occurs between o° and 100° C. suffers a diminution which may be expressed by a formula Vt = -c (t − e) where Vt is the velocity of the stream at a temperature t, and the critical temperature of water, and c a constant. It is argued that this result forms a measure of the tensile strength of the liquid, and consequently it brings the phenomenon of hissing into relation with the other properties of a liquid.

"Ionisation Potentials of Mercury, Cadmium, and Zinc, and the Single and Many lined Spectra of these Elements." By J. C. MCLENNAN, F.R.S., and J. P. HENDERSON.

1. It is shown that a spectrum consisting of a single line is obtainable for mercury, for zinc, and for cadmium.

2. The wave-lengths of these lines are for mercury λπ 2536 72 A.U., for zinc λ = €3075'99 A.U., and for cadmium A = 3260°17 A.U.

3. The minimum ionisation potentials for mercury, zinc, and cadmium are shown to be 49 volts, 3'74 volts, and 3.96 volts respectively.

4. Some considerations are presented which support Sir J. J. Thomson's theory of the two-type ionisation of atoms of mercury, and others which suggest that the theory is applicable as well to the ionisation of atoms of zinc and cadmium.

5. The minimum arcing potential differences which will bring out the many-lined spectra of mercury, zinc, and cadmium vapours are found to be 12.5 volts, 11.8 volts,

and 15.3 volts respectively. These voltages are also probably the minimum ionisation potentials of the second type for the atoms of these three elements.

6. Considerations are presented which suggest the possi bility of analysing the spectrum of an element in such a way as to enable one to correlate different portions of the spectrum with disturbances in definite portions of the atomic structure of that element.

"The Monoclinic Sulphates containing Ammonium.” Completion of the Double Sulphate Series. By A. E. H. TUTTON, F.R.S.

double sulphates of the series R2M (SO4)2.6H2O, in which In this communication are described the five remaining R is ammonium and M is nickel, cobalt, manganese, the author's work on the double sulphates of this series. copper, and cadmium. The present memoir completes The main conclusions are the following.

1. These ammonium salts are truly isomorphous with the similarly constituted potassium, rubidium, and cæsium salts of the generic formula above given, but are not eutropic with them; the potassium, rubidium, and cæsium salts alone form the exclusive eutropic series in which the crystallographical properties (both morphological and physical) obey the law of progression with the atomic weight of the alkali metal which has been established in previous communications. This law is particularly well illustrated by the fact, to which no exceptions have been observed, that average change of angle between crystal faces, and also maximum change of interfacial angle (which exceeds two whole degrees), are directly proportional to change to atomic weight when any one alkali metal is replaced by another.

2. The dimensions of the space-lattice of any ammonium salt of the series are nearly identical with those of the intermediate rubidium salt, so that the two atoms of rubidium are replaced by the ten atoms of the 2NH4 radicle groups without appreciably altering the crystallographic structural dimensions.

3. The salts of the series in which R is thallium (also studied in a previous memoir) resemble the ammonium salts closely, in truly belonging to the isomorphous series, but not to the more exclusive eutropic series formed by the salts of potassium, rubidium, and cæsium. Like the ammonium salts they also closely resemble the rubidium salts, but the thallium salts are distinguished optically, possessing transcendent refractive power, both their refractive indices and their molecular refraction being far higher than for any other salts of the whole isomorphous

series.