70 



POPULAR SCIEISrCE ITEWS. 



[May, 1889. 



will become cheaper than iron. There are 

 certain theoretical considerations which, we 

 think, will always render the reduction of 

 aluminium a costly process, although it has so 

 many important uses and valuable properties, 

 that "cheap aluminium" would be of inesti- 

 mable value to mankind, to say nothing of 

 the fact that every clay bank furnishes an 

 abundant supply of the ore. We shall await 

 with interest future developments in this line. 

 Sodium unites with mercury, forming 

 sodium amalgam, which is used in extracting 

 gold from its ores, and is also a valuable 

 laboratory reagent, especially in investigations 

 upon the hydro-carbon compounds. It also 

 forms a liquid alloy with potassium, which is 

 principally of theoretical interest. When 

 Humphrey Davy, almost a hundred years 

 ago, first produced a few grains of these metals 

 of the alkalies, he had little idea of the prac- 

 tical importance of his discovery, and, in 

 fact, ten years ago the inetals were rarely seen 

 .outside of a laboratory, and were principally- 

 used for the performance of the paradoxical 

 experiment of "setting water on fire." 



These sulpho-chlorides, moreover, are very stable ; 

 they are almost perfectly insoluble in water, and 

 may be digested with water in sealed tubes at 200° 

 C. without undergoing any change. They are also 

 insoluble in both hydrochloric and nitric acids, but 

 dissolve in tlie mixture of the two known as aqua 

 regia. They were finally shown to be distinct 

 chemical compounds, and no mere mechanical mix- 

 tures of sulphur and chloride, by the peculiar action 

 of potassium iodide upon them. It ni.iy, therefore, 

 be considered that the question of the action of sul- 

 phuretted hydrogen upon mercuric chloride has now- 

 been definitely settled. — Nature. 



THE ACTION OF HYDRIC SULPHIDE UPON 

 MERCURIC CHLORIDE. 



Three new sulpho-chlorides of mercury have been 

 isolated by Drs. Poleck and Goercki, of Breslau. 

 Every student of chemical analysis is familiar with 

 the peculiar changes of color which occur when a 

 solution of mercuric chloride is precipitated by sul- 

 phuretted hydrogen gas ; how that the precipitate at 

 first is perfectly w-hite, shortly passes to a yellow, 

 and then rapidly darkens, becoming orange, brown- 

 ish-red, and finally, when excess of the gas has been 

 led through the solution, perfectly black. The 

 white compound first formed was shown so long ago 

 as 1828 by Rose to consist of a sulpho-chloride of 

 the composition 2lIgS.HgCl2; but the further 

 changes appear never to have been hitherto 

 thoroughly investigated. The Breslau chemists, 

 after fully confirming the composition of the white 

 substance, now show that the darkening is due to 

 the formation of successive higher sulpho-chlorides, 

 SHgS.HgCls; 4HgS.HgCl2; sHgS.HgCl,,; the 

 final product being, of course, the sulphide of mer- 

 cury, HgS, itself. This has long been supposed to 

 be the case, and it is very satisfactory to have these 

 various sulpho-chlorides at last isolated. It may 

 readily be seen, however, that by simply passing 

 the current of sulphuretted hydrogen until the pre- 

 cipitate became of any particular tint, one would 

 never be able to isolate these highercompouuds, the 

 mixture becoming more complicated every minute. 

 The method adopted, after many fruitless attempts, 

 consisted in completely precipitating in various 

 experiments quantities of mercuric chloride corre- 

 sponding to three, four, and five molecules, respec- 

 tively ; the precipitates were in each case transferred 

 to a flask fitted with inverted condenser, and digested 

 for some time with a fresh quantity of the chloride 

 corresponding to another molecule. The first pro- 

 duct, 3HgS.HgCl2, possessed a brownish color, 

 and the two higher ones more and more nearly 

 approximated to the black of the pure sulphide of 

 mercury. In each case the filtrate was found to be 

 free from quicksilver and chlorine, proving that the 

 extra molecule of the chloride had in each case com- 

 bined, and analysis showed that the precipitates 

 really possessed the compositions above indicated. 



IS THERE MORE THAN ONE ELEMENTARY 

 SUBSTANCE .' 

 Analogy forbids us to believe that, down to a cer- 

 tain limit of dimensions that we call molecules, the 

 constitution of matter is of a wholly diflerent sort 

 from that which appears on sub-dividing the mole- 

 cules. It is an equally incredible assumption that 

 all atoms of the same element are so many inde- 

 pendent creations exactly alike in every respect. 

 Then, as our knowledge increases, the distinctions 

 between the chemical elements are becoming less 

 marked and their relations to each other more inti- 

 mate. They are beginning to appear, not as isolated 

 units, but as links in a complex network, which 

 presents an unbroken continuity throughout. The 

 recent study of the rarer earths leaves us in doubt 

 whether we have an indefinite number of elements, 

 or only one under unnumbered manifestations; and 

 the later results of spectrum analysis seem to indicate 

 quite clearly that, at the high temperatures of the 

 sun and the fixed stars, many of our terrestrial ele- 

 ments are decomposed. From a mathematical analv- 

 sis of the spectra, Grunwald maintains — and sup- 

 ports his conclusion by a remarkable array of con- 

 firmatory measurements — that the remarkable solar 

 spectrum line called helium, and the equally well- 

 marked line of the sun's corona, come from two 

 constituents of hydrogen gas, the first of which is 

 somewhat heavier and the last far lighter than 

 hydrogen gas. — Prof. Josiah P. Cooke, in the Pop- 

 ular Science Monthly. 



THE WHITENING OF BRICK WALLS. 

 The unsightly efflorescence on walls, due to what 

 is termed "saltpetring," and noticed generally in dry 

 weather, is due, according to Building News, to sev- 

 eral causes. Perhaps the only satisfactory explana- 

 tion is, that the newly built brick wall is exposed to 

 dampness, or dampness in co-operation with some- 

 thing in the bricks themselves. It is stated that 

 bricks made from clay containing iron pyrites are 

 subject to this efflorescence ; that the sulphur from 

 the fuel converts the lime or magnesia into sul- 

 phates, and that whenever the bricks dry, the sul- 

 phates evaporate, leaving behind the crystalline 

 appearance or efflorescence. The evil is therefore 

 due to the chemical action that takes place between 

 the sulphur in the fuel and the magnesia in the 

 clay. The mischievous part of the efflorescence is 

 that it destroys the pointing, and injures the work 

 generally. Remedies are few. The chief object is 

 to stop up the pores with some solution of fatty mat- 

 ter, quick-lime, and cement powder; but the main 

 thing is to avoid the particular clay and coal fires 

 employed to make and burn the bricks, and to mix 

 the mortar with animal fat. 



of the kind were caused by the shutter in front of 

 the lens not being properly adjusted, so that it acted 

 more or less as a diaphragm, besides which the lens 

 would not be whollv uncovered. 



It has long been agreed by good operators that 

 the best position for an instantaneous shutter is 

 immediately- in front of the sensitive plate, and the 

 only reason why the plan has not been more gen- 

 erally followed is on account of the slightly increased 

 mechanical difficulties involved. It is well worth 

 while, however, to take a little extra trouble in the 

 matter if the best results be aimed at. 



As high an authority as Mr. William England 

 said, during the meeting of which we speak, that 

 when using a roller-blind shutter next to the plate, 

 he had found that a slit of less than a quarter of an 

 inch in width in the blind was quite eifective. If 

 the traction upon the blind was made sufficiently 

 strong, immense r.-.pidity could be obtained. — 

 Science. 



r-t*1 



PRACTICAL RECIPES. 



For an Expansive Metal, melt together nine 

 parts lead, two parts of antimony and one part bis- 

 muth. 



French Rouge. — Powdered soapstone, 100 parts; 

 carmine, (number 40), aViparts ; water of ammonia, 

 (10 per cent), 20 parts. Treat the carmine in a mor- 

 tar with the water of ammonia. When it is dis- 

 solved, add the soapstone in small quantities at a 

 time with thorough trilmation. 



Useful Cements. — For mending valuable glass- 

 ware, use a cement made with five parts gelatine to 

 one part of a solution of acid chromate of lime. 

 Cover the broken edges w ith the cement, press the 

 parts together, and expose to sunlight. The light 

 hardens the cement, which will then withstand 

 boiling water. — For sticking leather, paper or wood 

 to metal, use glue to which has been added a little 

 glycerine— say a tablespoonful of glycerine to a gill 

 of glue. This is a good cement for fastening labels 

 to cans. 



Marking Ink. — The following was recommended 

 some years ago, as being indelible, and requiring 

 no heat : Phosphate of manganese, i oz. ; hydro- 

 chloric acid, I oz. ; anthracene, Vi oz. ; potassic 

 chromate, Hi oz. ; gum arable, q. s. ; water, 'A oz. 

 The phosphate to be dissolved in the acid, and the 

 anthracene added in the water and potassic chro- 

 mate ; add the gum and shake. Write with any 

 pen. Aniline black is also used for the same pur- 

 pose, thus: Nigrosine, 27 grains; hydrochloric 

 acid, 60 drops; alcohol, 45 drops. The mixture is 

 diluted with a hot solution of 40 grains of gum in 6 

 fluid ounces of water. 



Indian Ink. — B. Piffard, in Chemical News, gives 

 the following process, the result of which, he says, 

 seems to be identical with what is sold as India ink, 

 so far as the general uses to which it is applied. 

 An excess of camphor is placed in sulphuric acid, 

 and at the end of twenty-four hours there is a gela- 

 tinous mass <Jf a slightly reddish color. When this 

 is heated it effervesces, giving oft" fumes of sul- 

 phurous acid, and turns intensely black. By evapo- 

 ration, the excess of camphor and acid is driven oflf. 

 The remaining mass has the color and appearance 

 of India ink. When a portion is placed in water it 

 is entirely soluble. 



INSTANTANEOUS PHOTOGRAPHY. 

 At a recent meeting of one of the English Photo- 

 graphic Societies, it was stated that unless a consid- 

 erable portion of the lens was uncovered during the 

 instantaneous exposure, the whole of the image 

 would not appear on the plate. It was claimed that 

 the indistinct weak margins sometimes seen in work 



INDUSTRIAL MEMORANDA. 



A metallurgist gives as a reason why steel w ill 

 not weld as readily as wrought iron, that it is not 

 partially composed of cinder, as seems to be the case 

 with wrought iron, which assists in forming a fusi- 

 ble alloy with the scale of oxidation formed on the 

 surface of the iron in the furnace. 



