498 Scientific Intelligence. 



investigation using still greater proportions and more concen- 

 trated solutions of copper sulphate at similar temperatures. It is 

 to be regretted that the authors did not fully analyze the basic 

 sulphates that they prepared by simply heating aqueous solutions 

 of copper sulphate of widely varying concentration. Their 

 results, 66*34, 67-00 amd 68-21 per cent of OuO, although they 

 regard the composition as " highly influenced by the concentra- 

 tion of the solutions," show fairly good agreement for a com- 

 pound that cannot be recrystallized, and the average corresponds 

 closel}' to the formula 8CuO.S0 8 .2B a O, which they have suggested 

 for another product. — Jour. Amer. Chein. Soc, xxxviii, 1947. 



H. L. W. 



5. The Determination of Chlorides in Presence of Thiocf/- 

 anates. — It was shown several years ago by Rosanoff and Hill 

 that thiocyanates can be destroyed by suitable treatment with 

 nitric acid, leaving chlorides unattacked in a condition suitable 

 for determination by Volhard's volumetric method. F. W. 

 Bruckmiller has now shown that this treatment will permit the 

 determination of chlorine by the use of silver nitrate and chro- 

 mate indicator, particularly in water analysis. His process is as 

 follows: The solution containing chlorides and thiocyanates is 

 heated to boiling and concentrated nitric acid added drop by 

 drop, the amount depending upon the thiocyanate present. If 

 present in large quantities the nitric acid is added until the solu- 

 tion turns light brown. For small quantities 2 to 3 CC are suffi- 

 cient. The solution is boiled for 15 minutes and filtered if 

 sulphur has separated, and after cooling is neutralized with 

 normal ITNaC0 3 solution using methyl orange as indicator. A 

 little more than enough for neutralization is added, then after 

 adding the chromate indicator silver nitrate solution is added to 

 the usual end point. It was shown by experiment that there was 

 no loss of chlorine by boiling solutions containing -015 s of 

 sodium chloride after adding from 1 to 5 CC of nitric acid in 

 volumes varying from 100 down to 25 cc . It was shown further 

 that hydrocyanic acid was so far removed in the operation as not 

 to interfere with the process, and that the titration in the presence 

 of the methyl orange was accurate. — Jour. Amer. Chem. Soc, 

 xxxviii, 1953. H. L. w. 



6. A New Method of Determining Refractive Indices. — 

 Since the usual methods for making accurate determinations of 

 refractive indices require special preparation (prismatic form) of 

 the specimen to be tested and since it sometimes becomes neces- 

 sary to investigate figured objects (lenses) or fragments of 

 irregular shape which may not be cut, the new method of general 

 applicability recently worked out and tested by R. W. Cheshire 

 merits attention. It is based on the " Schlierenmethode " of 

 Topler. 



The following objects are arranged along a straight line. First 

 a source of monochromatic light. Then an opaque screen with a 

 vertical straight edge. An achromatic lens (focal length 125 cm , 



