352 ANALYSIS OF URINE. [CH. XIII. 



Example. 10 cc. standard silver = 20-2 cc. of stock KCNS. 

 So i cc. dilute KCNS = ^| = i -06 mg. Hg. 



2 cc. of diabetic urine taken. Mercury in ppt. required 24-2 cc. KCNS. 



So mercury = 24-2 x 1-06 = 25-65 mg. 



So total acetone in 2 cc. = 25-65 x 0-0606 = 1-55 mg. 



So total acetone in 100 cc. = 1-55 x 50 = 77-5 mg. 



NOTES. i . The original description gives a different method of standard- 

 ising the thiocyanate solution, by titration against a solution of mercuric 

 sulphate, which itself is standardised gravimetrically. 



2. The total amount of acetone bodies, reckoned as acetone, can usually 

 be arrived at by multiplying the figure found by the above analysis by 4-5, 

 but this can only be regarded as a rough approximation. 



I. Chlorides. 



The usual method for the estimation of chlorides in urine is Volhard's, 

 which is described on page 199 in connexion with the estimation of gastric 

 juice. The method given below is precisely similar. The silver nitrate 

 solution employed is of a different strength and the thiocyanate is not made 

 up to any defined concentration, but standardised against the silver. If 

 preferred the solutions described on page 199 can be employed, i cc. of the 

 o-i N. silver nitrate being equivalent to 0-00355 gram, of chlorine and 0-00585 

 gram, of sodium chloride. If this weaker silver solution is used, 25 or 30 cc. 

 of it should be taken for 10 cc. of urine. 



A method that is rapid, convenient and accurate, is that of Larrson, 

 but it is now difficult to obtain satisfactory charcoal. Recently, however, 

 the author has been presented with a specimen of charcoal that was prepared 

 for use in gas masks. It seems to be an extremely good absorbent, superior 

 to the best German products and admirably adapted for all kinds of analy- 

 tical work. The method is described in the hope that a satisfactory product 

 will soon be on the market. In that case Volhard's method would be super- 

 seded by Larrson's. 



412. The estimation of chlorides by Volhard's method. 



Principle. See page 199. 



Reagents required. 



1. Standard silver nitrate solution prepared by dissolving 29-063 grams, 

 of pure fused silver nitrate in distilled water and filling up accurately to one 

 litre. The solution should be kept in the dark. 



i cc. corresponds to -01 gram. NaCl (-00606 gram. Cl). 



2. Solution of potassium thiocyanate made by dissolving 8 grams, of the 

 salt in a litre of distilled water. 



3. Pure nitric acid, quite free from chlorine. 



4. A concentrated solution of iron alum. 



