1906.] The Chemistry of Globulin. 135 



that the whole of the additional salt c—c is occupied in keeping the 

 precipitate down. This solvent power proportional to (1 -\-p) c acting on the 

 precipitate p will give a rate of solution of the precipitate proportional to 

 p (1 +p) Co, and this must be equal to the rate of precipitation when 

 equilibrium is reached. But as*c— c is occupied in keeping the precipitate 

 down, the simplest assumption to make is that the rate of precipitation is 

 proportional to c— c Q . Hence, for equilibrium, 



^(l+^) = F(c-cb), (6) 



where F is a parameter characteristic of each salt. 



This equation of equilibrium is of the same form as (5). The precipitate 

 in this case is probably not globulin, but a compound of globulin and the 

 salt. It begins to come down at a concentration about 40 times that which 

 produces complete solution of the original globulin. But Mellanby's data for 

 MgS0 4 cannot be expressed by an equation like (5). They could be represented 

 by portions of two straight lines. 



When a salt of a heavy metal is added to a solution of globulin in a neutral 

 salt, the strength of the neutral salt being kept constant in all the comparisons, 

 the fraction of the total globulin precipitated is proportional to the amount 

 of the salt of heavy metal up to a certain point. 



Thus, with globulin dissolved in 0*6 per cent. NaCl and then precipitated 

 with ZnS0 4 , also dissolved in 06 per cent. NaCl, so that the total amount of 

 globulin in 10 c.c. was always the same, the fraction p of the globulin precipi- 

 tated is given by 



p = 2730c, (7) 



up to c = 0*000125 gramme per cubic centimetre, c being here the grammes 

 of ZnS0 4 per cubic centimetre of the 10 c.c. used. From c = 0'000125 to 

 c = 0-000225 the formula is 



j>-0-35 = 1030(c-0-000125). (8) 



Mellanby converts these two lines in his graph into a single curve, but 

 with some violence to the experimental data. For a solution of globulin 

 containing 0'0027 gramme NaCl per cubic centimetre and ZnS0 4 as 

 precipitant, p = 236 c up to c = 0-001, while from c = 0'001 to e = 0-0035 

 we can write p — 045 = 82 (c — 0-001). 



For CuS0 4 the corresponding equations are^? = 3660 c up to c = 0-00015, 

 and^ - 0-55 = 2000 (c - 0*00015) up to c = 0'00025. 



In this connection it is interesting to review the considerable amount of 

 analytical work done on the albuminates of the heavy metals.* Harnack 

 found, in 1881, that copper albuminate precipitated from excess of albumin 



* See F. N. Schulz, ' Die Grosse des Eiweissmolekiils,' Jena, 1903. 

 VOL. LXXIX. — B. M 



