BY DR. LAUDER BRUNTON. 427 



tion. If a precipitate is formed by boiling and is unchanged 

 by the nitric acid, or if one forms after the addition of the 

 acid, the fluid contains albumin. 



The acid is added for two reasons, (a) To dissolve any 

 substance wluck_iiug4fc be present in the solution, and being 

 precipitated by boiling might simulate albuminous coagula- 

 tion. Such substances are calcium phosphate which is present 

 in human urine, and calcium carbonate in the urine of herbi- 

 vora. As this test is very frequently used for detecting albu- 

 min in urine, these substances might very easily lead to error. 

 Albumin which has been coagulated by heat is not soluble in 

 nitric acid, and if the precipitate produced in the fluid by 

 boiling disappears on the addition of acid, no albumin is 

 present. 



(b) To neutralize alkali which might hinder the albumin 

 from being~precipitated by boiling. 



Take some solution of albumin jin water, add a few drops of 

 liquor potassse and boil. No precipitate occurs. Add one 

 drop of dilute nitric acid any precipitate which forms disap- *' 

 pears on shaking the tube. Add sufficient to make the fluid 

 very distinctly acid, and a permanent coagulum will be pro- 

 duced. The quantity of acid added must therefore not be too 

 small, or some albumin may remain in the solution. Some- 

 times, instead of using nitric acid, the fluid is kept boiling, 

 and acetic acid added very gradually till the fluid is neutral. 

 Unless very great care is taken to neutralize the fluid exactly, 

 this method may fail, for if an excess of acetic acid be added 

 it will retain the albumin solution. If neutralized exactly, 

 the albumin will be precipitated, and may be separated from 

 the fluid by filtration. 



2. Acidulate the fluid strongly with acetic acid, and then 

 add several drops of a solution of potassium ferrocyanide. If 

 albumin be present, a white flocculent precipitate will occur. 



3. Add acetic acid to the fluid till it is very distinctly acid, 1 

 mix it with its own volume of a strong solution of sodium sul- 

 phate, and heat to boiling. If albuminous bodies are present, 

 a permanent precipitate w5.ll be formed. 



This last method enables us not only to discover albumin 

 when present, but to separate it from the solution, so that 

 tests for other substances, such as sugar, with which the pres- 

 ence of albumin would have interfered, may then be applied 

 to it. 



11. Separation of Albuminous Bodies from other 

 Substances in solution. 1. The usual way of separating 

 albuminous bodies from solutions is by boiling, so as to coagu- 

 late the albumin. If the g^jpHmia tii'fl ^''^nily ooi ' 1 i they are 

 boiled without adding anything, but if not, a little dilute 



