26 ORGANIC CONSTITUENTS. 



acetates of lead^ sulphate of iron, clilorine, iodine, and bromine. 

 The following substances also give well-marked precipitates, 

 which are, however, soluble in an excess of the test, alum, sulphate 

 of copper, nitrate of silver, percliloride of iron, and nitrate of the 

 protoxide of mercury. Creosote produces an immediate tur- 

 bidity, and renders a solution of chondrin gelatinous in the 

 course of twelve hours. Alcohol throws down chondrin from 

 a concentrated solution, in the form of a white, viscid, and 

 tenacious mass. Ferrocyanide and ferridcyanide of potassium 

 throw down no precipitates when added to an acid solution of 

 chondrin. 



Glutin may be obtained in a state of purity from common 

 glue, of which it forms the chief ingredient. On placing glue 

 in cold water it absorbs moisture, and swells into a tremulous jelly, 

 but does not dissolve. The cold water must be changed as long as 

 it continues to take up anything from the glue. The glue, after 

 undergoing this purification, must be heated till it is perfectly 

 fluid, and then strained through a cloth or coarse filter. It ge- 

 latinizes on cooling, and when dried represents pure glutin. In 

 its physical characters it is nearly identical wdth chondrin, but 

 is usually rather more coloured. It is represented by the for- 

 mulai Cj3 H,^ N„ O^. (Mulder.) Scherer assigns to it the 

 formula C„g H^., N,. O,,., Avhich is numerically equal to 

 2 Pr + 3 NH^ 4- HO + 70, but recent investigations tend to show 

 that this formula gives an excess of hydrogen. AVhen burned, 

 glutin leaves a slight ash, consisting chiefly of phosphate of lime. 

 By long continued boiling, glutin loses its power of gelatinizing ; 

 in this state its ultimate composition may be represented by the 

 formula q^ H^, N^ O,^, or 4 (C,3 H^„ N^ OJ + HO. In other 

 words, it appears to be changed into a compound, in which four 

 equivalents of glutin are united with one of water. If a stream 

 of chlorine be passed through a solution of glutin, a compound 

 of chlorous acid and glutin is obtained, which is analogous in 

 type with the preceding substance. It is represented by the 

 formula 4 (C,3 H,^ N„ OJ +C1 O.. This is the compound re- 

 ferred to in the note to page 9. 



The most important test for gelatin (either glutin or chondrin) 

 is tannin, which Avill precipitate it when diluted 5000 times. 



' See Appendix I, Note 14. 



