Illaj 13, 1880] 



NATURE 



47 



merely the ordinary phenomenon of solubility of a solid in a hot 

 liquid. This view is borne out by their o\\ n experiments. They 

 found that on reducing pressure, that is, on allowing the liquid 

 to change to gas, the solid precipitated ; and also on heating the 

 tube containing the solution locally, that is, by converting the 

 liquid near the heated point into gas, precipitation took place. 

 I have tal^en the liberty of repeating one of their e.xperiments 

 with a slight modification. 



A tube shaped like that used in Experiment 3, after a small 

 fragment of potassium iodide had been placed in the lower com- 

 partment, was filled w ith nearly anhydrous alcohol ; and after 

 rather more than two-thirds of the alcohol had been evaporated 

 under reduced pressure, the tube was sealed. The lower portion 

 of the tube contained a strong alcoholic solution of potassium 

 iodide, besides a small piece of undissolved salt. The upper 

 portion of the tube was free from alcohol, but its walls were 

 incrusted w ith a thin crystalline film of potassium iodide. The 

 tube was heated in a sloping position, the liquid being in the 

 lower half. After the meniscus had disappeared, the iodide in 

 the lower half of the tube dissolved, while the film in the upper 

 half, even in its thinnest portions, remained unchanged. On 

 cooling, very sparkling crystals deposited in the lower half of 

 the tube, but no glittering crystals in the upper half. 



By repeated distillation the iodide in the upper portion of the 

 tube was washed down into the lower half, and when dry the 

 sides of the upper tube were quite bright and clean. The tube 

 was again heated in the same position to 20° above the tempera- 

 lure at which the meniscus had disappeared. On cooling, the 

 sparkling crystals again appeared in the lower tube, but not a 

 trace in the upper tube. To eliminate all possibility of mistake 

 the experiment wa; repeated five times with the same result, and 

 finally the ale ihol was distilled into the upper tube ; it was then 

 broken off, and its contents carefully tested for iodine with 

 sodium hypochlorite and starch-paste. There was not the 

 faintest blue colour, and it is therefore certain that potassium 

 iodide is absolutely insoluble in alcohol vapour. 



Messrs. Hannay and Hogarth also found that the absorption 

 spectrum of coloured salts remains unaltered, even when the 

 liquid in which they are dissohed loses its meniscus. Surely no 

 clearer proof is needed to show that the solids are not present as 

 gases, but are simply solutions in a liquid medium. 



To eliminate any source of error dependent on the use of 

 methyl formate, two other substances were employed, viz., 

 carbon disulphide, C.S„, and carbon tetrachloride, CCI4. The 

 former of these liquids was rectified five times over sodium, and 

 then boiled at 487 (corr.). The latter was rectified four times 

 over phosphoric anhydride, and boiled constantly at 77*5 (corr.). 



They yielded the following results : — 



Tube more Tube less 



than half full. than half full. 



CS„ 2827 286-4 



CClj 283-3 288-4 



These readings are given for the first appearance of a cloud in 

 the tube on cooling, and differ from the temperature at which the 

 meniscus disappears by being about half a degree lower. They 

 al-o do not represent extreme instances, for in the first cases the 

 liquids do not entirely fill the tube, and in the second about half 

 an inch of liquids remains in the tubes before it becomes im- 

 possible to distinguish liquid from gas. 



The experiments described in a former part of this paper, 

 relating to the difference of refraction shown by a liquid above 

 its so-called critical point, and the gas evolved from it, were 

 repeated with carbon tetrachloride and carbon disulphide, and 

 held g lod in both case^ The phenomena observed differed in 

 no particular from those already d; cribed. 



In conclusion, a few remarks on the liquefaction of the so-called 

 permanent gases may not be deemed out of place. If the deduc- 

 tions from the above experiments be correct, it follows thnt that 

 form of matter which we call gas may be converted into liquid 

 by pressure alone ; but the meniscus will never become visible, 

 for the pr.icess of change is a gradual one. To render the 

 meniscus visible it is necessary to take advantage of the fact that 

 liquids under such circumstances have a much greater coefficient 

 of expansion by heat, and conversely, a much greater coefficient 

 of c jutraction on withdrawal of heat, than gases. It therefore 

 becomes nece-sary to lower the temperature until the liquid by 

 contraction acquires a specific gravity greater than that of its 

 gas, and then, and not till then, does the phenomenon of a 

 meniscus become observable. 



April 29. — "On the Diurnal Variation in the Amount of 



Carbon Dioxide in the Air." By George Frederick Armstrong, 

 M.A., F.G.S., C E., Professor of Engineering in the Yorkshire 

 College, Leeds. Communicated by Prof. Thorpe, F.R.S. 



Summarising the results contained in this communication, it 

 may be stated — 



1. That the normal amount of carbonic acid present in the 

 air of the land is distinctly less than that usually stated, and that 

 it does not exceed 3-5 vols, in 10,000 of air. 



2. That plants absorb carbonic acid during the day and exhale 

 it at night, and that vegetation therefore alTects the quantity of 

 carbonic acid present in the air, decreasing it by day and 

 increasing it at night. 



3. That from this cause there is, during that part of the year 

 when vegetation is active, at least 10 per cent, more carbonic 

 acid present. in the air of the open country at nij;ht than during 

 the day. 



Chemical Society, May 6. — H. E. Roscoe, president, in 

 the chair. — The following papers were reid :— On the action of 

 sodium on phenylic acetate, by W. H. Perkin, jun., and W. 

 Hodgkinson. Hydrogen, acetic ethrr, phenol, acetic acid, 

 salicylic acid, a white crystalline .sub tance melting at 48° C, 

 having the composition Ci5Hi„03, and a yellow crystalline sub- 

 stance melting at 138°, havmg'the composition CigHj^Oj, were 

 obtained ; by heating cresylic acetate and sodium, acetic ether 

 and salicylic acid were formed. — Preliminary notice on the action 

 of sodium on some ethereal salts of phenylacetic acid, by Dr. 

 Hodgkinson. The first products of this action are the corre- 

 sponding ethylic, cS:c., ethers of phenylacetic acid. The phenyl 

 group being replaced by hydrogen, it reacts with sodium on 

 another portion of the original ethereal salt, forming various 

 liquid and solid bodies, which the author has investigated, but 

 whose constitution is as yet undetermined. — On the determina- 

 tion of nitrogen in carbon compounds, by C. E. Groves. The 

 author described and exhibited an improved and sim]>le appara- 

 tus for facilitating the collection and measurement of the nitro- 

 gen evolved during the combustion of a substance according 

 to Dimias' method. — On essential oil of sage, by M. M. P. 

 Muir. The composition of this oil varies with its age, salviol 

 and camphor being formed as it gets older. English sage-oil 

 contains cedrene. The terpene of sage-oil is identical with that 

 of French turpentine. The author has examined the action of 

 oxidising agents, phosphorous pentachloride, and bromine. — On 

 the presence of nitrogen in iron and steel, by A. H. Allen. By 

 passing steam over iron at a red-heat, and also by dissolving iron 

 in hydrochloric acid, the author has satisfactorily proved that 

 ammonia is formed equal to 0-0041 to 0-0172 parts of nitrogen 

 per hundred parts of iron and steel. — On the mode of applica- 

 tion of Pettenkofer's process for the determination of carbonic 

 acid in expired air, by Dr. W. Marcet. The author de-crifies 

 and figures a portable apparatus which he has successfully used in 

 upwards of 350 determinations of carbonic acid made during 

 some investigations on the effect of altitude on the phenomena of 

 respiration. — On an improved form of oven for heating sealed 

 tubes and avoiding risks of explosions, by Watson Smith. — Note 

 on a convenient form of lead-bath for Victor Meyer's apparatus 

 for determining the vapour-densities of high boiling substances, 

 by Watson Smith, 



Anthropological Institute, April 27. — Major-General A. 

 Pitt-Rivers, F.R.S. , vice-president, in the chair. — Edward Tyrrell 

 Leith, LL.M,, was elected a new memlier. — A paper entitled 

 ** Further Notes on the Romano-British Cemetery at Seafonl, 

 Sussex," by Mr. F. G. Hilton Price and Mr. John E. Price was 

 read. It was a continuati n of one read bef re the Institute by 

 the same authors in November, 1876. During the summsr of 

 1S79 these gentlemen again visited Seaford, and made further 

 excavations in the Roman Cemetery upon the Downs, in which 

 they discovered several urns, a drinking cup of Durobrivian 

 pottery, Samian paterje, flint celts of the neolithic lype, and 

 many flint flakes. In one particular interment a larsje urn fu I 

 of charred human bones was discovered, having a .Sau.ian cup 

 in its mouth for the purpose of keeping out the earth, another 

 cup of elegant form of Durobrivian ware was found on its left 

 side, and a food vessel and patera of Upchurch pottery on the 

 right side. In close proximity to this interment was a similar 

 one ; the urn w.as much crushed, but beneath a patera of Samian 

 ware a coin of Faustina Junior, the daughter of Antoninus Pius 

 and wife of Marcus Aurelius, was found. This was most im- 

 portant as giving an approximate date t<i the interments ; they 

 could not be earlier than between A. D. 161 • 180. In another 



