70 



Messrs. B. Moore and W. H. Parker. 



soaps as is obtained in the saponification of beef fat. When snch a 

 mixture is submitted to the solvent action of the bile it is found that 

 more sodium oleate than palmitate or stearate is taken up, as is shown 

 in the considerable reduction which is obtained in the melting point of 

 the mixture of fatty acids dissolved and re-obtained from the bile as 

 compared with the melting point of the fatty acids obtained from the 

 mixed soaps before being acted upon by the bile. In fact, it is only 

 when sodium oleate is also present that sodium palmitate and stearate 

 are taken up by the bile in appreciable quantity. As a result of this, 

 the figures obtained by this method, in the case of the mixed sodium 

 soaps, must only be taken as indicating the maximum amount of soaps 

 which the bile is capable of taking up from such a mixture at body 

 temperature, and it must be remembered that the portion taken up has 

 not the same composition as the mixture extracted, and that the solu- 

 bility of the residue gradually decreases as the percentage of palmitate 

 and stearate in it increase.* 



The second method, which has chiefly been used in making the 

 determinations, is to add the substance to be dissolved in small weighed 

 portions at a time to a measured volume of the solvent contained in a 

 test-tube and kept at body temperature by being immersed in a water 

 bath provided with a thermostat. The mixture is stirred from time to 

 time with a glass rod, and the substance to be dissolved is rubbed up 

 with the solvent to hasten the process of solution. The amount added 

 when solution ceases to be complete is noted, and from this a close 

 approximation can be made to the percentage solubility. The approxi- 

 mation is the closer the smaller the amount of substance added each 

 time, and the larger the volume of solvent which is taken. By using 

 10 c.c. of solvent and adding the substance in portions of O'Ol gramme 

 at a time, it is thus possible to determine the solubility within one-tenth 

 of a per cent. The method is somewhat laborious in making a first 

 determination from the number of weighings, but in later determina- 

 tions with the same solvent and solute it can be shortened by adding 

 at once nearly the total quantity which it is known will be dissolved. 

 Reliable results are obtained by this method in the case of determining 

 the solubility of pure substances, but in a mixture of the soaps it gives 

 a lower result than the total amount which the solvent will take up 

 from the mixture, because the signal for stopping is here that point at 

 which the maximum amount of the least soluble constituent of the 

 mixture has been taken up. Thus a slight residue is obtained when 

 even as little as 0'5 per cent, of mixed sodium soaps is added to bile at 

 body temperature, and a somewhat heavier residue when water is 



* A similar result is seen -when the mixed fatty acids or soaps obtained by 

 saponifying any naturally occurring fat are treated with a solvent in winch fchey 

 are not exceedingly soluble, such as hot alcohol, a residue of insoluble stearic acid 

 or stearate is finally obtained. 



