THE CHEMICAL NEWS

VOL. CX., No. 2865.

MECHANICAL LIQUID FEEDER. By F. H. LORING.

ENGINEERS, of course, know that, to perform an exceedingly simple mechanical act continuously, regularly, and in such manner as to be acceptable in widespread commercial practice, very considerable elaboration of device often becomes necessary. Such elaboration should

scum that may be present, especially when by accident the

dregs of a tank get into the supply pipe. Moreover, the

precision of the feed, which is under perfect manual control, is a great advantage. Syrupy liquids, as well as ordinary liquids, can be easily fed by this method under conditions of varying back-pressure or resistance.

A certain amount of mechanical elaboration, however, was found necessary to carry into practice this simple idea, and the working-drawing (quarter reduction from full size) here reproduced, shows this device which I have termed a feeder, as it is used for feeding liquids into specially designed centrifugal machines. Referring to the front elevation, the worm and shaft-bearings are shown in superposed section. In the plan the rubber tubing and the clips are omitted, and the details of the foot part are not shown.

In the section through A-B a roller is outlined to show

be the means of ensuring a minimum of attention and trouble in the long run.

The problem of delivering small regulatable quantities of acidulated liquid day and night continuously without fail, and without variation due to careless manipulation or other causes, is not quite such an easy one as would appear upon first consideration.

After trying plunger-pumps which leaked and developed valve troubles, gravity-feeds with restriction tubes or taps, which clogged and were often wrongly adjusted notwithstanding indexes provided, to say nothing of breakages and sundry mishaps. I finally hit upon the simple scheme of pushing the liquid along by rolling a standard soft rubber tube. This method has the great advantage of not involving the use of a device which can become clogged or inoperative from a thickening of the liquid, or from any

the proper distance between the rollers and the bottom of the groove.

These feeders were originally tested by keeping them in more or less continuous operation day and night in different places for upwards of six months, and no trouble of any kind developed.

Step-pulleys are provided for four changes of speed, each step representing a known definite feed of liquid material through the tube. The other pulley, not shown in the drawing, is mounted on a light countershaft. Pure black commercial soft rubber tubing of best quality is employed, which remains in good condition for several months; should renewal be necessary, the cost is quite insignificant. The kneading action of the rollers does not appear to destroy the life of the rubber, and it is indeed surprising how many kinds of acids and corrosive salts in

solution may be pumped or fed by this device without causing appreciable deterioration of the rubber for at least a reasonable length of time. Of course some acids are destructive. These feeders are manufactured in considerable quantities, and may be purchased at reasonable prices on application to the writer.

30, Norfolk Street, Strand, London, W.C.

IS SILICA AN INDISPENSABLE CONSTITUENT OF PLANT FOOD?

By MARSHALL LUNDIE.

THE use of farmyard manure as a fertiliser was known to man long before letters existed by which it could be recorded. We begin to get records of some agricultural practices in Roman times. Even then not only the value of dung was known, but also the virtues of other manures, such as marl, were established. The great poet Virgil in his works makes reference to the fertilising effect of a crop of vetches, or lupins, upon the succeeding wheat crop. To whatever point the knowledge of manuring had reached in the time of the Romans, for a long time it made no progress. In the mediæval times agriculture took a step forward; the value of chalk, woollen rags, ashes was generally known. The experience of men of an enquiring turn of mind had built up a certain knowledge of manures and manuring, and had even begun to reason a little on the mode of action of these manures. In spite of the experience that was accumulating respecting the fertilising value of this or that substance, no real progress was made towards a theory of manuring until the beginning of the nineteenth century.

Before the development of the science of chemistry it was naturally impossible to form any idea as to how a plant came to grow, while the nature of the plant itself, of

the air, water, and earth were equally unknown; no correct opinion could be reached as to how the latter gave rise to the former.

The true theory of the nutrition of plants begins soon after the discovery of the composition of the air. Priestley observed that plants possessed the power of purifying air rendered defective by combustion or by the respiration of animals, and he having been the discoverer of oxygen, it was found that the gas which leaves gave off was oxygen. It was further demonstrated that light was essential for the development of these phenomena, while the oxygen was proved to be derived from the carbonic acid taken up, and that the gain in weight of the plant was practically represented by the carbon, combined with the elements of water, forming chiefly starch and sugar.

Such great scientists as Sir H. Davy, de Saussure, and I.iebig took this important subject in hand, but it is to the latter that we must attribute the chief impulse which agricultural chemistry has received, for he drove home to the minds both of scientific men and of farmers the true theory of plant nutrition. He laid down the general principle that the carbon compounds, which constitute more than

95 per cent of the dry substance of most plants, are derived by the plants from the atmosphere, and that if the plant be supplied with the 2 per cent or so of mineral constituents which are found in the ash, it will then draw upon the atmosphere for all the materials the crop ultimately contains. These views of Liebig, coming at a time when great interest was directed towards agriculture, and backed by his great scientific reputation, aroused instant and widespread attention, being the foundation both of practical experiment and scientific research.

The ashes of a large number of plants were analysed, and the natural conclusion was drawn that all these ash constituents found were essential to plant growth, and were of equal importance. In the majority of cases the percentage of silica in the ashes was found to be very high, even amounting to as much as 50 and 60 per cent.

From this it was generally thought that silica was one of the chief constituents of plant food, and experiments were made using sodium silicate as a fertiliser, and the following, from A. D. Hall's " Fertilisers and Manures," p. 271, will show how far people went in drawing conclusions:

"Silica is so large a constituent of the ash of many plants, particularly of the straw of cereals, that it was inevitably regarded as a necessary constituent of the food of such plants, and was naturally enough supposed to contribute to the stiffness of the straw. In his manure Liebig supplied the alkalis combined with silica, and when Way discovered that certain strata of the Upper Greensand, near Farnham, contained considerable quantities of silicates readily dissolved by acids, the rock was for a time extracted and ground up as manure for cereals."

Sir Humphry Davy's theory regarding the part that silica played in the plant was that it gave the plant a certain firmness, but he overlooked the fact that the leaves of the grasses which do not help to support the plant contain much more silica than the stems, and hence his theory

cannot be correct.

At this time many exaggerated ideas were held as to the ammonia present in the atmosphere; the rain was believed to bring down as much as 30 to 40 lbs. per acre per annum of combined nitrogen instead of the 3 to 4 lbs. which we now know to represent the true quantity. This was due to imperfect methods of analysis. A great deal of controversy took place, some holding that it was unnecessary to use nitrogenous manures, as sufficient nitrogen as ammonia in the rain was supplied for the requirements of the plant. demonstrated experimentally, the yield being, in fact, The necessity of a supply of combined nitrogen was roughly proportioned to the amount of combined nitrogen added as manure. If only the mineral constituents of the ash were supplied, the crop fell away rapidly as soon as the reserves of active nitrogren in the soil had become exhausted, and it was further demonstrated that the ordinary plants were incapable of utilising the full nitrogen of the air, but only took up nitrogen in a combined form from

the soil as manure.

manures, experiments also settled in a practical fashion In addition to establishing the value of nitrogenous pensable to the plant and were necessary constituents of a the question of which of the ash constituents were indiscomplete manure.

The fundamental necessity of phosphoric acid and potash, and the non-essential nature of soda, magnesia, and silica as manure constituents were soon established. the plant food was carried out first by Liebig by means by The synthetical method of determining the character of water cultures, with the result that the following nine substances were found to form the indispensable constituents of plant food, viz. :—

plant, which cannot be performed by the other constituents.

It was at this time that Leibig enunciated the great Law of the Minimum, which states that if one of the necessary ingredients of plant food is provided in insufficient quantities, the plant takes up of the other necessary constituents only so much as is in a definite proportion to the quantity which is supplied in the minimum amount.

From these results it was clearly shown that silica, sodium, and chlorine were not indispensable, although it is a well established fact that barley, figs, and buckwheat thrive on a brack soil.

The author has carried out a series of water culture experiments with wheat, in order to demonstrate the nonessential nature of silica.

The experiment was carried out in the following manner: A number of wheat grains were soaked over night, then put into a germinating dish (Professor Nobbe's apparatus) on May 31, 1911. It was observed on June 3 that they had commenced to germinate. Three of the most healthy were selected for the experiment. Nos. I and 2 were put into the water culture solution on June 8, while No. 3 was put in on the following day.

The water culture solution was made up as follows:In 1 litre of distilled water was dissolved

By kind permission of Dr. Hahn these experiments were carried out in his greenhouse, where the plants were safely protected from the strong winds. On calm days they were put outside and exposed to the direct rays of sunlight.

Grasses.

No. I

No. 2

Sweet grasses..

• 365

Summer

Sour

33.2

Bran

Winter wheat (young plants)

Oats (young plants)

..

27 6

Maize (flowering plant)

Summer rye 54'1

124

Oats

52'0 46.7

24 24

31 43

54

5*

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No. 3 The solutions had to be filled up every day with distilled water, owing to the transpiration current through the plant of water which enters by the root hairs, and is eventually evaporated from the leaves and other growing surfaces of the plant. This amount became considerable when the plant became full grown. On a warm day as much as 500 cc. was observed to be the decrease in volume

of the culture solution. The solutions in which the young plants were growing were frequently shaken up so that more air, and hence oxygen, could be dissolved.

On July 12, August 26, September 9, September 29, October 12, fresh water culture solution was put in. These growing plants were carefully watched, and if at any time a fungus was noticed on the cork or cotton wool, these would be immediately replaced by fresh sterilised material.

The height to which these plants grew, and the enormous number of stems and leaves produced in each case, were very striking-in fact, they looked more like bushes, and gave one the impression that they were making full use of the food material supplied, and were not sparing

Some of the seeds of these water cultures were put in a germinating dish, and after a few days were observed to germinate.

We have now completed the life cycle of one of these wheat plants, and have shown the non-essential part silica plays as a nutritive.

The silica is deposited in the cell membrane, and being in the epidermis of the plant supplies a certain protection from fungi (rust) sending its mycelium roots into the leaf.

I have it on Dr. Hahn's authority that a number of years ago a series of water culture experiments were being carried out at the South African College Chemical Laboratory, when they became attacked by rust, and in two days every plant was overrun with the fungus. This clearly offer no resistance to the ravages of such pests as rust. shows that when the plant is deprived of its silica it can

Here in South Africa we have a fine sunny climate, where everything thrives well, including the pests.

As to how and to what extent silica in a plant repels the attacks of fungoid growth is, indeed, a subject offering a wide field for research, and being of such great importance to us South Africans, surely this matter should be taken up and thoroughly investigated by our biologists.

It is well known that the silica in soils derived from

granitic rocks is less soluble than the silica which is derived from doleritic and basaltic rocks. In the granitic rocks the silica exists as pure quartz, and as trisilicate in felspar and mica, whereas dolerite and basalt do not contain free quartz, and their constituent silicates like hornblende, augite, anorthite, are disilicates and monosilicates.

Since the silica in the granitic soils is less soluble than silica in the dolerite and basaltic soils, one cannot help thinking that the cereals which are such great silica eaters will take advantage of this when grown on doleritic or basaltic soils, and will contain more silica in the ashes than the cereals grown on granitic soils. If the theory is correct that the presence of silica in the cereals renders the plants more resisting to the attacks of fungoid growth, the cereals grown on dolerite and basaltic salts should suffer less than the cereals grown on granitic soils, provided that climatic and weather conditions are the same.

These are questions of such economic importance to South Africa that they should receive full attention at the hands of those who are carrying on research in connection with the production of cereals in our country.-South African Journal of Science, ix., No. 10.

THE DEHYDRATION AND RECOVERY OF SILICA IN ANALYSIS.

By F. A. GOOCH, F. C. RECKERT, and S. B. KUZIRIAN.

The Dehydration of Silica.

THE question as to the temperature which must be applied, and of the duration of the ignition necessary to bring silica to a constant weight in the analysis of silicates, has been the subject of much investigation and discussion. The opinion is general that in order to obtain the correct weight of anhydrous silica derived by precipitation in the usual course of analysis and ignition, the temperature employed must be that of the blast-lamp (Hillebrand, Journ. Am. Chem. Soc., xxiv., 371; Treadwell, "Quant. Anal.," trans. Hall, 3rd ed., p. 486). Lunge and Milberg (Zeit. Angew. Chem., 1897, p. 425) have shown, however, that silica obtained by hydrolysing silicon fluoride sustains after ignition in the full flame of a good Bunsen burner no further appreciable loss upon application of the blast heat, and these results have been confirmed by Lohöfer (cf. Hillebrand, loc. cit.) in Lunge's laboratory, and by Hillebrand, for silica thus derived from silicon fluoride. On the other hand, Hillebrand found in the case of silica derived by fusing quartz with sodium carbonate, treating the product with hydrochloric acid, and evaporating three times, with intermediate extractions and filtrations, that constant weights were obtainable only by blasting, and that blasting for half-an-hour (as is generally recommended) is often insufficient to secure constancy of weight. Quartz powder was used as the source of the silica in Hillebrand's experiments, and this was found to be 99.88 per cent pure, by careful treatment with sulphuric and hydrofluoric acids.

It has been shown recently in certain experiments by B. H. Walker and J. B. Wilson (U.S. Geol. Survey, Circular No. 101, August 16, 1912) that silica precipitated by acid may be brought to a constant weight by prolonged ignition over the Bunsen burner, thus avoiding the danger of loss which may occur when platinum is submitted to prolonged ignition with the blast-lamp. Three hours is the minimum period mentioned as requisite. It is to be noted, however, that in these experiments no test was made for impurity in the residue after ignition, and that, as will appear from the work to be described, the main source of trouble in bringing precipitated silica to a constant weight does not lie in the process of dehydration in ignition, but is due to the presence of an impurity which must either be volatilised or made to enter into stable chemical relation with the silica. From the results of certain experiments to be detailed it will appear that, while prolonged ignition

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05536 05536 0'5531 05531

(a) It was found that the crucible used in this determination was subject to loss when ignited by itself over the blast-lamp.

TABLE II.-Ignition of Silica separated by Acid after Fusion with Sodium Carbonate.

CAL

Silica taken (grm.).

After ignition Corrected

pure).

with Corrected blast by lamp HF+H2SO4 15.min. process. periods.

(a) 0.00013 SiO2 in 1 grm. Na2CO3.

The original material taken for our experiments was a commercial "analysed". hydrous silicic acid containing approximately from 45 to 50 per cent of anhydrous silica according to the degree of exposure. When digested with boiling water this material yielded traces of a soluble chloride and soluble sulphate. After the ignition of portions of the original substance-from 0'5 grm. to 5 grms. -for fifteen minutes over a large Bunsen burner, traces of chloride or sulphate could be still detected in the silica. When similar portions of the original substance were ignited over the burner for forty-five minutes or over the blast-lamp for half-an-hour neither chloride nor sulphate was found in the aqueous extraction of the residue, but treatment with sulphuric acid left a residue which amounted in the average to o 24 per cent of the original substance. The barium sulphate precipitable by barium chloride from the solution of this residue proved to be nearly equivalent to the entire residue counted as sodium sulphate. Inasmuch as neither chloride nor sulphate could be found in this strongly ignited silica, it may be presumed that sodium oxide, remaining in combination with the silica, constituted, at least after the strong ignition, the impurity which after the treatment with the acids appeared in the form of sodium sulphate. Upon this presumption, the silica used was 99'92 per cent pure after the strong ignition. The record of experiments in which portions of the hydrous silica were heated during successive half-hour periods, with the

Bunsen burner and with the blast-lamp, is given in Table I. These results show plainly that the silica used may be brought to a practically constant weight in half-hour ignitions with a good sized Bunsen burner.

The next experiments show the effects of treating similarly the product obtained by fusion of the ignited silica with sodium carbonate, treatment with hydrochloric acid, evaporation, extraction with very dilute hydrochloric acid, and careful washing. In Series A of these experiments the drying was effected at 110° in the air-bath. In Series B the residue obtained by evaporation to apparent dryness on the steam-bath was moistened with acetic anhydride, and warmed over a radiator until this reagent fumed freely, the object of this treatment being to thoroughly desiccate the silica while preventing the otherwise possible formation of sodium silicate by action between silica, included sodium chloride, and water. Each of these methods of treatment leaves the silica drier, more porous, and therefore more effectively washable than is the case when drying is brought about by the steam-bath only. The results of these experiments are given in Table II. Every residue of silica was treated after the final ignition with sulphuric acid and hydrofluoric acid, the amount of sodium sulphate remaining was weighed, and the equivalent weight of the combined sodium oxide was calculated.

A comparison of these results with those of Hillebrand,