492 A MANUAL OF PHYSIOLOGY 



Acetone. (i) Legal' s Test (Rothera's modification). To 5 to 

 10 c.c. of the acetone-containing urine add enough ammonium sul- 

 phate crystals to form a layer at the bottom of the test-tube, then 

 2 or 3 drops of a fresh 5 per cent, solution of sodium nitro-prusside 

 and i to 2 c.c. of strong ammonia. The development of a colour 

 like that of permanganate of potassium, often in the form of a ring 

 a little above the undissolved salt, indicates the presence of acetone. 

 The reaction must not be declared negative till half an hour has 

 elapsed. The colour slowly fades. 



(2) Where there is doubt as to the presence of acetone, it is 

 best first to distil it over. Put 250 to 500 c.c. of the urine suspected 

 to contain acetone into a litre flask. Add a few c.c. of phosphoric 

 acid ; connect the flask with a worm (see Fig. 180, p. 483), and distil 

 over the urine into a small flask. For qualitative tests it is best to 

 collect only the first 20 to 30 c.c., as most of the acetone is contained 

 in this. Test the distillate for acetone by (i) or by 



Lieben's Test. To a few c.c. of the distillate in a test-tube add a few 

 drops of solution of iodine in potassium iodide and then sodium or 

 potassium hydroxide. A precipitate of yellow iodoform crystals (six- 

 sided tables) is thrown down if acetone be present. Examine them 

 under the microscope. On heating, the odour of iodoform may be 

 recognised. If the precipitate is amorphous it may be dissolved in 

 ether (free from alcohol), which is allowed to evaporate on a slide, 

 when crystals may be obtained. 



Determination of the Freezing-point of Urine. Study Beckmann's 

 apparatus shown in Fig. 153, p. 399. Note the large thermometer D 

 graduated in hundredths of a degree centigrade. It is inserted 

 through a rubber cork into the inner thick test-tube A. A platinum 

 wire F, bent at the lower end into a circle or a spiral, which passes 

 easily up and down between the bulb of the thermometer and the 

 tube, serves to stir the urine. The thermometer must be so supported 

 by the rubber cork that the bulb is in the axis of the tube and a 

 centimetre or two from the bottom of it. The side-piece E on the 

 tube A is not absolutely necessary, but it is convenient for ' inocu- 

 lating ' the urine with a crystal of ice at the proper time. A passes 

 through a rubber cork into a shorter and wider outer glass tube B. 

 The space between A and B serves as a badly conducting mantle, 

 which prevents too rapid cooling of the contents of A. B passes 

 through a hole in the metal or wooden cover of a strong glass jar C, 

 which contains the freezing mixture. B should fit the hole so tightly 

 that it does not bob up out of the mixture when A is removed. In 

 C is a stirrer, G, of strong copper wire, the end of which passes through 

 the lid. This serves to stir up the freezing mixture from time to time. 

 Pulverize some ice by pounding it in a strong wooden box with 

 a heavy piece of wood. Take the inner tube with the thermometer 

 out of the apparatus. It is convenient to take the thermometer 

 out of the tube, and to hang it up carefully on a stand by means of 

 a fine flexible copper wire passing through the eye. The rubber cork 

 can be taken out with the thermometer, and the platinum wire also, 

 the bent free end of the latter supporting it in the cork, or it may be 

 fastened temporarily to the thermometer stem by a small rubber 

 band, which is slid up over the cork when the thermometer is re- 

 inserted. Tube A can be set temporarily in a specially heavy test- 

 tube rack. Remove the lid of C, and with it tube B. Now put ice 

 and salt alternately into C until it is nearly full, mixing them up well. 

 Add some cold water from the tap till the stirrer G can move freely 



