COMPOSITION OF THE PROTEIDS. 27 



result will be achieved, when proteids obtainable in a crystalline form 

 have been thoroughly investigated. 



Vegetable proteids have been prepared in a crystalline form 1 in 

 combination with magnesia; Drechsel 2 found in one preparation 14 per 

 cent, of magnesia (MgO) ; in another, prepared by an improved method, 

 143 per cent. From this the molecular weight x may be calculated as 

 follows : 



a; _ 100 -143. 975 . 

 40 143 



From the similar examination of the sodium compound the mole- 

 cular weight of albumin was found to be 1496. Other vegetable pro- 

 teids examined by Griibler 3 also gave high but variable molecular 

 weights. 



Haemoglobin belongs to the proteid compounds capable of crystallisa- 

 tion; Zinoffsky 4 prepared haemoglobin crystals from the blood of the 

 horse in a very pure state, and the formula calculated for haemoglobin 

 from his elementary analyses would be 



If a molecule of haematin, C 32 H 32 N 4 4 Fe, is subtracted, the formula for 

 proteid left is 



241 



Jaquet's 5 formula for pure haemoglobin of dog's blood would give the 

 proteid molecule a formula 



C726-"- 117 i-N 194 S 3 O 214 



So that here again there are great discrepancies. 



Such a summary of the principal analyses made, is quite sufficient to 

 give point to Drechsel's conclusion, that while divergences of analysis 

 exist, even though they are due to extremely small errors, it is futile 

 to attempt to measure accurately the size of the proteid molecule. 

 Drechsel points out that in so large a molecule an analytical error of 

 O'Ol per cent, would have the same importance as one of 01 per cent, in 

 ordinary analyses. 



It should be added, in conclusion, that some few investigators have 

 used the cryoscopic method in attempting the solution of this problem ; 

 the molecular weight of egg-albumin by this method is 14,000 

 (Sabanejeff), 6 of albumoses 1200-2100, and of antipepton much less 

 (Paal). 7 



Equally inconclusive, though much more interesting, have been the 

 attempts to discover the rational formula for the proteid molecule. The 



that proteids in solution will not pass through a membrane of gelatin or silicic acid, when 

 filtered under pressure. The products of proteolysis (proteoses and peptones) will, 

 however, pass such a membrane ; the smaller size of their molecules has also been demon- 

 strated by the cryoscopic method. Crystalloids pass through such membranes at the same 

 rate as water, and can thus be easily separated from colloids in a solution containing both 

 (C. J. Martin, Journ. PhysioL, Cambridge and London, 1896, vol. xx. p. 364). 



1 The subject of vegetable and crystalline proteids will be treated at length in a later 

 section of this chapter. 



' 2 Journ. /. prdkt. Chem., Leipzig, 1879, N.F., Bd. xix. S. 331. 



3 Ibid., 1881, Bd. xxiii. S. 97. 



4 Ztschr. f. physiol. Chem., Strassburg, 1885, Bd. x. S. 16. 5 Inaug. Diss., Basel, 1889. 



6 Ber. d. deutsch. chem. Ge*dlach., Berlin, 1891, Bd. xxiv. Ref. 558. 



7 Ibid. , 1894, Bd. xxvii. S. 1827. For Siegfried's work on the identity of antipeptone 

 with a simple compound, which he has called carnic acid, see under " Chemistry of Muscle," 

 p. 103. 



