URINE. 137 



for from 36 to 48 hours. Uric acid crystals of a whitish- gray, 

 or more commonly of a red colour, deposit themselves from this 

 acid urine, partly at the bottom and partly on the sides of the 

 glass. The mass of the clear supernatant fluid must be poured 

 off, the crystalline coating is then loosened from the sides of 

 the vessel, and collected on a small filter. When all the uric 

 acid is collected on the filter, and the whole of the fluid has 

 run through, a little water is sprinkled over it, and the filter 

 is then dried and weighed. By subtracting the known weight 

 of the filter, we obtain the amount of uric acid. 



5. Determination of the water- and spirit -extracts. 



From 1000 to 2000 grains of filtered urine are evaporated 

 on the water-bath, and the residue treated with alcohol of 0*83, 

 which throws down the water extract, as well as the sulphates 

 and phosphates. These are collected upon a weighed filter, and 

 washed with alcohol of similar strength. The filter with its 

 contents is weighed, and by deducting the known weight of 

 the filter, we obtain the weight of the water-extract and salts. 

 By incineration of the filter and its contents, there are left only 

 the sulphates and phosphates; the water-extract is, therefore, 

 estimated by the loss. 



Whatever is dissolved by the alcohol of 0'83 is mixed with 

 the spirit used for washing, and the fluid gently evaporated 

 on the water-bath until an extract-like residue is left ; this, after 

 being allowed to cool, (during which process it usually becomes 

 solid,) is treated with cold anhydrous alcohol. In this way the 

 spirit-extract, as well as chloride of sodium, and a portion of 

 the alkaline lactates, if any are present, are separated. The 

 basin is kept as cool as possible, and repeated additions of ab- 

 solute alcohol are made, in order to see whether the alcoholic 

 solution which has become clear after settling, still becomes 

 turbid, and if so, a certain quantity of anhydrous alcohol must 

 again be added. When the alcoholic fluid (A) is perfectly clear, 

 it is decanted from the residue of salts, which is washed with 

 anhydrous alcohol, cautiously dried on the water-bath, weighed, 

 and estimated as spirit-extract with salts. By a thorough in- 

 cineration we can determine the spirit-extract by the loss of 



