194 SCIENCE PROGRESS 



monoxide ; the gas is not produced by enzymatic decomposi- 

 tion, since it is only formed in the hving plant, and, moreover, 

 finely divided kelp in contact with sea-water gives only carbon 

 dioxide and hydrogen. The gas is considered to be a respira- 

 tion product of the plant, and not an intermediate product of 

 photosynthesis. 



In spite of the considerable time that has elapsed since 

 " Salvarsan " was first put on the market, conflicting views 

 have, from time to time, been expressed concerning the com- 

 position of the commercial product ; as the result of a re- 

 investigation of this question by Fargher and Pyman {J. Chem. 

 Soc, 1920, 117, 370), there appears to be no doubt that the 

 substance contains two molecules of water of crystallisation, 

 but is free from methyl alcohol, which had been stated by some 

 authors to be present ; its composition is therefore repre- 

 sented by the formula QaHiaOaNaAsa, 2HCI, 2HaO. Both the 

 British and German products contain from i to 2 per cent, 

 of sulphur, as an impurity, combined, most probably, in the 

 form of a sulphaminic acid or possibly merely physically ab- 

 sorbed. 



The view expressed by Blount {J. Chem. Soc, 1919, 115, 705), 

 that the colour of " Blue John " fluorite is of organic origin, is 

 confirmed by Garnett {ibid., 1920, 117, 620), who has shown 

 that the finely powdered substance on combustion gave a 

 carbon content of 0-27 per cent., while on subjecting the 

 material to distillation, a yellowish-brown oil collected in the 

 cool parts of the vessel, together with a mirror-like coating of 

 carbon, while a residue of colourless fluorite was left behind. 



In a paper dealing with the constitution of Cholesterol, 

 Windaus {Chem. Zentr., 1920, [i], 82) gives a possible formula 

 for this substance ; considerations of space preclude the print- 

 ing of this formula, but attention is drawn to it here as it is 

 more complete than any previously published formula for this 

 compound. 



CB.TSTALLOGB.AFHY. By Alexander Scott, M.A., D.Sc. 

 Crystal Structure. — In the section on Crystallography in the 

 Reports on the Progress of Chemistry, T. V. Barker {Ann. Rep. 

 Chem. Soc, 16, 197, 1920) gives a critical summary of recent work 

 on the elucidation of crystal structure by means of X-rays. The 

 various modifications of the original methods are discussed, and 

 the results obtained up to the present are summarised. The 

 view that the chemical molecule persists in the solid state is 

 upheld, but the argument that the fusion of crystals of, say, 

 an ortho-compound should result in the formation of a mixture 

 of ortho- and meta-molecules in the liquid state is scarcely 

 convincing. It is conceivable that, even if ** solid " molecules 



