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URINE: QUANTITATIVE ANALYSIS. 403 



hydroxide solution are added and the mixture (B) subjected to 

 redistillation. Distil off about 300 c.c. and titrate this distillate 

 (B 2 ) as usual with iodine and thiosulphate (see p. 399). 



Calculation. The author advises the use of solutions of thio- 

 sulphate and iodine which are a trifle stronger than T \, i. e., 103.4^. 

 Each cubic centimeter of an iodine solution of this strength is 

 equivalent to one milligram of acetone or to 1.794 milligram of 

 /?-oxybutyric acid. The thiosulphate solution is accepted as the 

 standard and should be restandardized, from time to time, by a 

 ~Q solution of potassium bi-iodate. 



2. Black's Method. Render 50 c.c. of the urine under examina- 

 tion, faintly alkaline with sodium carbonate and evaporate to one- 

 third the original volume. Concentrate to about 10 c.c. on a water- 

 bath, cool the residue, acidify it with a few drops of concentrated 

 hydrochloric acid 1 and add plaster of Paris to form a thick paste. 

 Permit the mixture to stand until it begins to " set," then break it up 

 with a stout glass rod having a blunt end and reduce the material to 

 the consistency of a fairly dry coarse meal. 2 Transfer the meal to a 

 Soxhlet apparatus and extract with ether for two hours. At the end 

 of this period evaporate the ether-extract either spontaneously or in 

 an air current. Dissolve the residue in water, add a little bone black, 

 if necessary, filter until a clear solution is obtained and make up 

 the filtrate to a known volume (25 c.c. or less) with water. The 

 /?-oxybutyric acid should then be determined by means of the 

 polariscope. 



3. Darmstadter's Method. This method is based on the fact 

 that crotonic acid is formed from /?-oxybutyric acid under the 

 Influence of concentrated mineral acids. The method is as follows : 

 Render 100 c.c. of urine slightly alkaline with sodium carbonate 

 and evaporate nearly to dryness on a water-bath. Dissolve the resi- 

 due in 150-200 c.c. of 50-55 per cent sulphuric acid, transfer the 

 acid solution to a one liter distillation flask and connect it with a 

 condenser. Through the cork of the flask introduce the stem of a 

 dropping funnel containing water. Heat the flask gently until 

 foaming ceases, then use a full flame and distil over about 300-350 

 c.c. of fluid, keeping the volume of liquid in the distillation flask 

 constant by the addition of water from the dropping funnel as the 

 distillate collects. Ordinarily it will take about 2-2^ hours to col- 



1 The residue should give a distinct red color with litmus paper. 

 " Before this is accomplished it may, in some cases, be necessary to add a 

 little more plaster of Paris. 



