238 ALBUMINOIDS. 



but emulsin does not attack myronic acid, nor does invertin 

 convert starch into maltose and dextrin, etc. It is easy, there- 

 fore, to detect diastase in malt, invertin in yeast, emulsin in 

 almonds, etc., the presence of which is anticipated. The liquefaction 

 of starch-paste, the conversion of cane-sugar into invert-sugar, the 

 development of hydrocyanic acid and oil of bitter almonds, are 

 changes so striking and so promptly effected, that the qualitative 

 detection of the ferments producing them leaves nothing to be 

 desired. But the varied natiu'e of the ferments themselves and 

 of their action renders it exceedingly difficult to detect them in 

 vegetable substances that have not previously been examined, as 

 a general reagent applicable . in «uch a case is yet unknown. It 

 must be admitted that attention has been drawn to the fact that 

 the ferments liberate oxygen from an aqueous solution of peroxide 

 of hydrogen, to which a little tincture of guaiacum has been 

 added, and thus produce a blue colouration of the mucture. But 

 it is hardly to be expected that this property should be shared by 

 all ferments, or that it should be peculiar to them alone. 



§ 231. Estimation of total Albumen. — The total albumen soluble 

 in water can be estimated by means of acetate of copper, provided 

 that no tannin or other substance precipitated by the same reagent 

 is present in solution. The precipitate produced by an excess of 

 the acetate is filtered off, dried, weighed, and ignited, the resulting 

 oxide of copper being deducted.^ 



If other substances are thrown down ■^th the albumen the 

 nitrogen in the priecipitate may be determined, and from that the 

 albumen present calculated. Eitthausen ^ and Taraskewicz * have 

 proved experimentally that the precipitate contains the whole of 

 the albumen, casern, etc. 



§ 232. Estimation con^mMed— Sestini* considers it advisaUe to 

 precipitate with acetate of lead. In cases in which other nitro- 



I In some instances it is necessary to add a considerable excess for complete 

 precipitation of the albumen. In an experiment made by Taraskewicz with 

 casein, 1 gram of oxide of copper (in the form «f acetate) was found to pre- 

 cipitate 4 '19 gram of casein; but for complete precipitation an amount of 

 acetate corresponding to 4 '55 grams of oxide had to be added. 



' Loc. (At. 34, etc. ; Bitthausen and Settegaat, Archiv f. d. ges. Phys. xvi. 

 293, 1877. See also Momer, Upsala Lakarefiiren. Forhandl. xii. 475, 1877 ; 

 Taasbender, Ber. d. d. chem. Ges. xiii. 1818, 1880 (Joum. Chem. Soc. xl 

 205). 



' Loc. di. 



* Landwirthsch. Versuchsst. xx. 305, 187o (Journ. Chem. Soc. xxxiv. 740). 



