198 ESSAY XVII. 



SECTION VI. 



No substance is more like curds than the white of 

 boiled. It is indeed nothing else but pure cheese. The 

 white of eggs coagulated by heat dissolves by means of 

 boiling in very diluted mineral acids, which solution is again 

 precipitated on adding some concentrated acid. During this 

 precipitation, there is likewise a smell, exactly like that of 

 hepar sulphuris, produced, which is a very singular pheno- 

 menon. Silver is coloured by it, and acetated lead rendered 

 black, properties all of which are likewise common to the 

 curds of milk (Sec. IV.). It is also a singular fact, though it 

 be generally known, that heat alone coagulates the white of 

 eggs, and this without any loss of its weight. The true 

 cause of this is, as far as rny information reaches, hitherto 

 unknown, but seems to me to be the following : As curds 

 and the white of eggs combine with acids, and are thereby 

 coagulated, and as all the substances which enter into a 

 union with acids may be likewise combined with the matter 

 of heat, a circumstance in which this principle often resembles 

 acids, it is very probable that it enters into a chemical union 

 with the white of eggs, and is thus the cause of coagulation. 

 What confirms me more in this opinion is, that I have 

 observed such a coagulation of the white of eggs produced 

 in the following manner : I mixed one part of white of eggs 

 with four parts of water, and added a small quantity of a 

 solution of caustic alkali, mixing at the same time as much 

 muriatic acid as was necessary for its saturation ; the white 

 of the egg then coagulated like curds. I mixed the water 

 with the white of eggs, with the view of preventing the heat 

 which is expelled by acids from caustic alkalies from becoming 



