I.] THE PROTEIDS. 3 



the salt, and shaking vigorously in a tube or flask. This precipi- 

 tates all protcids except peptones. Filter ; the filtrate contains no 

 proteids. 



(g. ) By hydrochloric acid in a solution saturated with common salt. 



(h.) By alcohol, except in the presence of a free alkali. 



(i.) Precipitate a portion with (i. ) meta-phosphoric acid ; (ii. ) phosphotung- 

 stic acid, after acidulating with HCl. 



N.B. — Peptones are not precipitated by (e.) and (/.). 



(C.) Coagulation by Heat. 



(,;.) Heat the fluid to boiling — there is no coagulum of albumin 

 formed — and then add, drop by drop, dilute acetic acid (2 per 

 cent.), until a flaky coagulum of coagulated insoluble albumin 

 separates. 



The coagulum comes down about 70° C. Unless the fluid 

 be acidulated, the albumin does not coagulate. 



(k.) Boil and add nitric acid = a white or yellowish coagulum. 



(I.) Acidify strongly with acetic acid, add an equal volume of 

 a saturated solution of sodic sulphate, and boil = coagulation. 

 This precipitates all proteids except peptones. This method and 

 the foregoing (J.) are used for separating the albumin in a liquid 

 containing it. 



(D.) (m.) IndifFusibility. — Place some of the solution either in 

 a dialyser or in a sausage-tube made of parchment-paper, and sus- 

 pend the latter by means of a glass rod thrust through the tube 

 just below the two open ends (Lesson IX.) in a tall glass jar filled 

 with distilled water, so that the two open ends are above the sur- 

 face of the water. The salts (crystalloids) diffuse readily (test for 

 chlorides by nitrate of silver and nitric acid), but on applying any 

 of the above tests no proteids are found in the diftusate. They 

 belong to the group of Colloid bodies. (Peptones, however, are 

 diffusible through animal membranes.) 



(E.) (n.) Reaction of Adamkiewicz. — To white of egg add glacial acetic 

 acid, and heat to get it in solution; gradually add concentrated sulphuric 

 acid = a violet colour with slight fluorescence. 



(0.) Liebermann's Reaction. — "Wash finely powdered albumin first with 

 alcohol and then with cold ether, and heat the washed residue with concen- 

 trated hydrochloric acid = a deep violet-blue colour. This is best done in a 

 white porcelain capsule, or on a filter-paper in a funnel ; in the latter case, 

 the boiling acid is poured gently down the side of the filter-paper. 



For other colour reactions with cobalt sulphate and NH4HO, and KHO see 

 Pickering, Journ. of Phys., vol. xiv. 



2. Presence of Nitrogen and Sulphur in Albumin. 



(a.) Place some powdered dried albumin in a reduction tube, 

 and into the mouth of the tube insert (i) a red htmus paper, 

 and (2) a lead acetate paper. On heating the tube, the former 

 becomes blue from the escape of ammonia, which can also be 



