§ 234. EXTRACTION WITH SPIRIT. 241 



of good pepsin to be taken for every 2 grams of finely powdered 

 substance. Starch, if present in large quantity, might with 

 advantage be previously converted into maltose and dextrin by 

 boiling, cooling to 40°, and digesting for four hours at that 

 temperature, after adding 0'005 gram of active diastase. 



§ 234. Extraction tvith Spirit. — Some of the albuminoids in- 

 soluble in water attract our attention by their solubility in spirit, 

 as, for instance, those known as glutenfibrin, gliadin (or vegetable 

 gelatine), and mucedin. In seeds only have these three substances 

 been detected with certainty ; they remain undissolved when the 

 material containing them is treated with water, or, at most, the 

 mucedin alone is partially taken into solution. They would be 

 removed, however, by the dilute alkali used for the extraction of 

 the glutencasein (§ 226), and it is advisable therefore, in looking 

 for these substances, to treat the material with spirit previously 

 to extracting the glutencasein with alkali. Part, however, of the 

 glutenfibrin and a little gliadin would be left undissolved, and would 

 be subsequently found with the casein (§ 226). The spirit should 

 be used cold, and should be of a strength of about 60 to 80 per 

 cent. The maceration must extend over a considerable period, 

 and the spirit be renewed several times. The united extracts are 

 distilled until the strength of the spirit is reduced to 40 to 50 per 

 cent, (not less). On cooling, a clear slimy mass separates, con- 

 sisting principally of glutenfibrin mixed with a few flocks of gluten- 

 casein and possibly fat (which is, however, better removed by 

 petroleum spirit before treating with alcohol). If the majority of 

 the spirit is distilled off from the clear liquor a second precipitate 

 will form, consisting principally of gliadin and mucedin, and a 

 further quantity of the same two substances (impure) can be ob- 

 tained by neutralizing the filtrate with a little potash and con- 

 centrating. 



All these precipitates are triturated with absolute alcohol until 

 they become hard and sohd.^ Fat, if present, is removed by 

 treatment with ether. 



We are as yet unacquainted with any method of separating the 

 glutenfibrin, gliadin, or mucedin for quantitative determination. 

 We must therefore content ourselves with making a total estima- 



^ The spirit dissolves a little cilutenßbrin, which can subsequently be precipi- 

 tated by ether. 



16 



