314 



SCIENCE- GOSSIP. 



» CHEMISTRY 



CONDUCTED BY C. AIXSWORTH MITCHELL, 

 B.A.OXON., F.I.C., F.C.S. 



New Explosive for the Services. —The 

 practical experience gained during the present war 

 in South Africa has at length led to the abandon- 

 ment of cordite. When in 1889 it was fir.st 

 adopted by the Government, scientific experts 

 pointed out that it was an unsuitable explosive 

 owing to its corrosive action upon the guns 

 and the difficulty of keeping it unimpaired in dif- 

 ferent climates. Soon after the war commenced 

 these defects in the explosive were naturally forced 

 into prominence. A Committee was then formed 

 to investigate the subject, presided over by 

 Lord Rayleigh, and including Sir Andrew Nobel, 

 Sir William Crookes, Sir W. Roberts- Austen, and 

 Mr. Haldane. Thns Committee has recently recom- 

 mended the disuse of cordite and the substitution 

 of a new explosive to be known as " Cordite M.D.," 

 or modified cordite. The old cordite consisted of 

 pure gun-cotton incorporated with 58 per cent, of 

 nitro-giycerin and 5 per cent, of vaseline by 

 means of a solvent (acetone) that was subsequently 

 evaporated. The paste was pressed out through 

 fine orifices into thin cords, which were reeled on 

 to drums, thoroughly dried, and cut into lengths. 

 The finished cordite was light to dark-brown in 

 colour and of the consistency of indiarubber. It 

 burnt with a strong flame, which could be readily 

 extinguished. The chief ingredient in the new 

 powder is nitro-cellulose. Nitro-glycerin, the 

 destructive agent in the old, is no longer employed. 



Detection op Formalin in Milk.— Numerous 

 tests have been described during the past few 

 years, some of which are so sensitive that they 

 will readily detect one part of formalin in 200,000 

 parts of milk. One of the simplest and most 

 characteristic is based upon the fact that a violet- 

 blue ring is obtained when milk containing traces 

 of formaldehyde is diluted with an equal quantity 

 of water and strong sulphuric acid poured upon 

 the surface. The reaction 'is not obtained with 

 absolutely pure sulphuric acid, but requires the 

 presence of a ti-ace of an oxidising agent, such as 

 iron chloride, nor is it given with stronger solutions 

 of formaldehyde— e.g. a liquid containing 0-5 per 

 cent. A second striking test for formalin is that 

 first described by Mr. Hehner. On adding one 

 drop of a very dilute solution of phenol (carbolic 

 acid) to the distillate from milk, and pouring the 

 mixture gently on to strong sulphuric acid, a 

 brilliant crimson ring is formed at the junction of 

 the two liquids, if the milk contained as much as 

 1 part in 200,000 of formaldehyde. 



Formalin on Flesh.— Referring to Mr C. A. 

 Mitchell's note on the action of formalin on flesh, 

 I should be glad if he would inform me what is 

 the least strength that will jDrevent bacterial 

 growth.- I have used a 2^ per cent, solution (that 

 is, 2i parts of the 40 per cent, commercial formal- 

 dehyde to 87| parts of water) for micro-slides, and 



have sometimes found a pure growth of bacteria 

 in the slides, though hermetically sealed. What 

 is required for micro-work is a watery fluid, not 

 appreciabh' denser than water, and as neutral as 

 possible, that will prevent bacterial growth and 

 preserve unaltered the tissues and protoplasmic 

 structures after they have fu'st been fixed by one 

 of the fixing agents. I should be glad if a chemist 

 would investigate this subject, and should like 

 also to know his opinion of a solution of sulphur 

 dioxide as a preservative, and what changes it is 

 likely in time to produce in tissues. What is 

 " Microbe Killer " ? It seems to preserve a piece 

 of fresh meat very well. I have tised bichloride 

 of mercury in — per cent, solution, with a little 

 common salt added, as a preservative, and after a 

 time very fine crystals, with a head at one end. 

 looking exactly like very fine pins, have appeared 

 in the hermetically - sealed slides. Can Mr. 

 Mitchell tell me what substance it is that forms 

 these- crystals ? — Charles F. Bmtssclet, 2 Peiubridgt 

 Crescent , Bay^n-nter. <S'. TF.. Jannarii dflt. 



[It is surprising that Mr. Rousselet should have 

 found bacteria in preparations preserved with 

 formaldehyde, for his experience is contrary to that 

 of most other observers. Possibly the bacteria 

 were there before the addition of formalin, or the 

 formalin solution was not of the strength supposed. 

 The extremely antiseptic properties of formal- 

 dehyde can be proved by adding a few^ drops of 

 the strong solution to 4 ozs. of milk and leaving 

 the corked bottle for some weeks, when it will still 

 be found perfectly fresh, with a thick layer of 

 cream upon the surface. It should not be difiicult 

 to find the right strength for a preservative 

 solution for microscope slides, though the only 

 sections I have preserved have been stained, treated 

 with clove oil, and mounted in Canada balsam. 

 The crystals observed by Mr. Rousselet were 

 probably a compound salt of mercuric and sodium 

 chlorides. I have never examined '• Microbe Killer,'' 

 and am therefore unable to speak as to its com- 

 position. — Ed. Chemistry.] 



Crystallised Glycerin. — If ordinary glycerin 

 be exposed to a low temperature for a long time, 

 small crystals, resembling sugar crystals, can often 

 be obtained. Apparently the ordinary product 

 contains the crystalline glycerin in a state of super- 

 saturation, for on introdiicing a few glycerin 

 crystals into the liquid at about the ordinary 

 temperature fresh crystals can rapidly be grown. 

 According to analyses by Mr. Otto Hehner, the 

 crystals which thus separate are pure anhydrous 

 glycerin, while the mothei--liquid that surrounds 

 them consists of glycerin containing about 6 percent, 

 of water. Werner was also able to obtain crystalline 

 glycerin by passing a few bubbles of chlorine into 

 concentrated commercial glycerin. When rapidly 

 exposed to very low temperatures, glycerin yields a 

 solid glass-like mass, as was found by Prof. Dewar. 

 Crystallised glycerin melts at 22° C.'(71°-r) F.), 



ANSWERS TO CORRESPONDENTS. 



P. F. — In reply to a query sent me by Mr. P. 

 Fell, I may state that it is not altogether an easy 

 matter to obtain the flashing of arsenic crystals on 

 separation from a hot solution of hydrochloric acid 

 (ante vol. vii,, p. 2y.S). It is necessary to re-crystal- 

 lise the arsenic trioxide repeatedly, as apparently 

 a slight trace of impurity is sufficient to prevent 

 the phenomenon. Once I failed to produce flashing 

 until after I had crystallised the arsenic five times. 



