84 INTRODUCTION. 



coagulation is not complete until the liquid has been brought 

 to the boiling point. It must be remembered, however, that 

 albumen is not coagulated by heat in an alkaline solution. 

 In testing the urine for albumen by heat, if the liquid be 

 alkaline it must be neutralized with a little acetic acid ; other- 

 wise there will be no coagulation, even if albumen be present 

 in abundance. There may also arise a source of error from 

 the precipitation by heat of an excess of earthy phosphates. 

 This precipitate is distinguished from albumen by the fact 

 that it is dissolved by a few drops of hydrochloric acid, while 

 coagulated albumen is not changed. Coagulated albumen 

 in urine is redissolved by the addition of a little potash, 

 which has no effect upon an opacity produced by the 

 phosphates. 



Another test is the addition to the suspected solution of 

 a strong mineral acid ; when, if albumen be present, coagu- 

 lation will take place. There is only one source of error in 

 the application of this test to the urine. If the urates be 

 present in very large quantity, we may have a deposit of 

 uric acid, giving an opacity something like that produced 

 by coagulated albumen. This error may be avoided by 

 adding an excess of nitric acid, which will clear up the mix- 

 ture if the deposit be due to the presence of urates, but has 

 no effect upon albumen. In such a case, also, no turbidity 

 is produced by heat. When uric acid is deposited, the 

 turbidity makes its appearance more slowly than when albu- 

 men is present. Various acid mixtures have been proposed 

 as tests for albumen, but they seem to possess no advan- 

 tages over nitric acid, which is the one most generally em- 

 ployed. 



The tests by heat and nitric acid are sufficient to deter- 

 mine the presence or absence of albumen in any clear 

 fluid, if applied with the precautions above indicated. We 

 may employ, however, coagulation by alcohol, or the albu- 

 minimeter of Becquerel ; but the latter, like the saccharom- 

 eter of Biot and Soleil, is little used on account of the 



