CH. XIII.] ACETONE BODIES. 349 



410. Acetone and aceto-acetic acid. This can be found 

 by difference between the two previous exercises, or it can be 

 determined separately by the method adopted for total acetone 

 bodies, except that (i) no dichromate is added, and (2) the boiling is 

 continued for not less than 30 nor more than 45 minutes. 



Calculation, i gram, of precipitate corresponds to 2-0 grams, of acetone 

 and aceto-acetic acid per cent., reckoned as acetone. 



NOTES. i. Van Slyke also gives a method of titrating the mercury 

 precipitate. It is presumably quicker, since it is not necessary to prepare and 

 dry the Gooch crucible. The author has no experience of it. 



2. The Gooch crucible should be of 25 to 50 cc. capacity, and fitted as 

 shewn on page 259. The asbestos mat can be prepared as described on page 

 132, except that it should be thicker than stated there. It is thoroughly 

 washed and firmly sucked down and dried in a steam oven or a hot-air oven 

 at 110 C. It is allowed to cool in the air and weighed. It is then fitted to 

 the rubber cup and some distilled water carefully added and sucked gently 

 through before the mercury precipitate is filtered off. Several precipitates 

 can be collected and weighed one after another. (See also p. 389.) 



3. The reagents should be tested by performing an experiment with 

 distilled water instead of urine, starting with the copper sulphate treatment. 

 No precipitate whatever should be obtained. Van Slyke gives a caution that 

 this test should not be omitted. 



4. A blank determination of precipitate from other substances in urine 

 ether than the acetone bodies may be made by following the procedure of 

 Ex. 409, except that 5 cc. of water are substituted for the dichromate and 

 the boiling period under the condenser is strictly limited to 45 minutes. The 

 weight of precipitate obtained is deducted from that found in any estimation 

 of the acetone bodies. It is usually so small that it can be neglected, except 

 in cases where only small amounts of the acetone bodies are present. 



411. The estimation of acetone and aceto-acetic acid in 

 urine by the method of Scott- Wilson.* 



Principle. The urine is distilled into an alkaline solution of silver 

 mercuric cyanide. The aceto-acetic acid is decomposed into acetone, which 

 passes over with any preformed acetone into the cyanide. An insoluble keto- 

 mercuric-cyanide compound is formed. This is filtered off, dissolved in acid, 

 and the amount of mercury determined by titration with standard thiocyanate. 

 From the amount of mercury present the total amount of acetone in the urine 

 taken can be calculated. 



Solutions required. 



i. Silver mercury cyanide. Dissolve 9 grams, of pure caustic soda and 

 0-5 gram, of mercuric cyanide in 60 cc. of distilled water. Add 20 cc. of 0-7268 

 per cent, silver nitrate slowly with constant stirring. If necessary filter 

 through a layer of washed asbestos in a Gooch crucible. The silver nitrate 

 solution is prepared by diluting 5 cc. of the standard silver nitrate used in the 

 next exercise with 15 cc. of distilled water. 



* Journ. of Physiology, xlii., p. 444. 



