2 CHEMICAL PHYSIOLOGY. 



(c.) To a third portion add a drop or two of very dilute 

 solution of cupric sulphate, and then a solution of caustic 

 soda (or potash) = a violet colour (Biuret Reaction). 



(d.) Make a fourth portion strongly acid with acetic acid, 

 and add potassic ferrocyanide = a white precipitate. 



(e.) Heat a portion of the neutral solution = a coagulum 

 about 70 C. 



(/".) To a solution of white of egg add glacial acetic acid, 

 and heat to get it in solution ; gradually add concentrated 

 sulphuric acid = a violet colour (The Reaction of Adam- 

 kiewicz). 



(g.) Wash finely powdered albumin first with alcohol and 

 then with cold ether, and heat the washed residue with con- 

 centrated 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 (Liebermann's Re- 

 action). 



(h.) Non-diffusibility of Proteids. Place some of the solu- 

 tion either in a dialyser, or in a sausage-paper made of 

 parchment-paper, and suspend the latter by means of a glass 

 rod thrust through the tube just below the two open ends, 

 as in fig. 10, in a tall glass jar or beaker filled with distilled 

 water, so that the two open ends are above the surface of 

 the water. The salts will diffuse readily (test for chlorides 

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

 the above tests no proteid will be found in the diffusate. 

 (Peptones, however, are very diffusible.) 



N.B. The reactions d, e, /, and g are not obtained with 

 peptones. 



Preparation Of Millpn's Reagent. Dissolve mercury in its own 

 weight of strong nitric acid, specific gravity 1 '4, and to the solution thus 

 obtained add two volumes of water. Allow it to stand, and afterwards 

 decant the clear fluid ; or take one part of mercury, add two parts nitric 

 acid, specific gravity 1 "4, in the cold, and heat over a water-bath till com- 

 plete solution occurs. Dilute with two volumes of water, and decant the 

 olear fluid after twelve hours. 



