8 ORGANIC CONSTITUENTS. 



casein) a gradual swelling ensues, and tlie substance assumes 

 a gelatinous appearance. On the addition of water it con- 

 tracts, and it is found to be perfectly insoluble in tbat fluid. 

 It must be collected on a filter and boiled in water as long 

 as a solution of baryta indicates that any sulphuric acid is 

 being given ofl": it must then be heated with alcohol, and 

 dried at a temperature not exceeding 260°. This is siilpho- 

 proteic acid. It appears as a yellow mass, is not easily pul- 

 verized, and is insoluble in water, alcohol, and ether, but dis- 

 solves in potash and ammonia. The salts of silver, copper, 

 lead, and iron yield precipitates Avith the alkaUne solutions of 

 this acid. Its formula is C,^^ H„ N, O,,,, SO^. 



On the cautious addition of dilute siilphuric acid to an 

 acetic acid solution of protein, we obtain ]Mulder's sulpho-hi-pro- 

 teic acid, which is then thrown down as a flocculent precipitate. 

 After washing it, and diying it at a temperature not exceeding 

 260°, it assumes a white appearance, and may be easily pulve- 

 rized. With the alkahes it forms solutions from which many 

 of the metallic salts throw down insoluble compounds. Midder 

 considers that it is composed of two atoms of protein, two of 

 water, and one of sulphuric acid ; hence it may be expressed 

 by the formula C,„ H,,, N,„ O.^, + H.^ O,, + SO3. 



If protein (or any of its modifications) be boiled in dilute 

 sulphuric acid, a beautiful purple tint is evolved. 



j3. Hydrochloric acid and protein. Mulder has formed a hydro- 

 chloro-jyroteic acid in the same manner as the sulpho-proteic 

 acid. Its formula is C^„ H,„ N,^ 0,^^ + H.^ O.^ + H CI. WTien 

 protein is boiled in strong hydrochloric acid the solution is at 

 first yellow, but it gradually merges into a blue tint. This 

 change of colour does not occur if the atmospheric air is ex- 

 cluded. 



-y. Nitric acid and protein. On the addition of nitric acid to 

 protein or to any of its modifications, nitrogen and a little nitric 

 oxide are evolved, oxalic acid and nitrate of ammonia are formed, 

 and there remains undissolved a bright yellow matter, which on 

 being dried assumes an orange tint, and which is known as 

 Xantho-proteic acid. It is devoid of smell and taste, although 

 it slightly reddens moistened litmus paper. It is insoluble 

 in water, alcohol, and ether. It dissolves in strong mineral 

 acids, but is precipitated on the addition of water ; with the 



