Dr. E. J. Mills on Elective Attraction. 507 



The nitrates to which this particular method of determining 

 chemical activit}^ applies must, as necessary conditions, be capable 

 of perfect desiccation and actually amenable to the influence of 

 the oxychloride. It was also advisable to exclude the nitrates 

 derived from ammonia, amines, and amides, inasmuch as the 

 employment of these would have rendered indispensable a pre- 

 liminary inquiry into the phosphamides — bodies whose formulse 

 are for the most part at present unknown, but which would 

 almost certainly occur, and have to be quantitatively determined 

 in a mixture already sufficiently complex. Omitting baric 

 nitrate, upon which, when it is dry, phosphoric oxychloride is 

 without action, there appears, then, reason to believe that « can 

 be satisfactorily valued in eight instances only. 



Apparatus. — The preparation of a supply of air free from 

 every trace of moisture is a well-known difficulty which has 

 seldom been very satisfactorily overcome. For the purpose of 

 these experiments an apparatus was eventually constructed 

 w^hich was found to answer every requirement. Seven glass 

 vessels were filled to about one third of their capacity with pumice 

 free from chlorine and supersaturated with oil of vitriol, and 

 were connected with caoutchouc tubing both to each other and a 

 gas-holder containing air. A wash-bottle containing oil of 

 vitriol was added to these, to serve as a time-indicator; and the 

 arrangement terminated with a long tube containing phosphoric 

 followed by baric oxide. The volume of the air contained in 

 this apparatus was at least four times as great as was required 

 in any individual experiment. By closing it at both ends for 

 twenty-four hours, the whole of the internal moisture would be 

 removed ; and on admitting a small stream from the gas-holder, 

 it seemed highly probable that dry air only would leave the ap- 

 paratus, even during the course of an entire operation. 



The next portion consisted of a narrow inverted U-tube, which 

 was followed by the '^reaction-tube,^' wherein the cheuiical pro- 

 cess was actually carried out. The latter, which had the shape 

 of an ordmary " Liebig's drying-tube '■' (the body of which held 

 about 7 cubic centims.), was used also for weighing the neces- 

 sary materials, during which operation it was closed with a glass 

 stopper and a caoutchouc fastening; in the process its body was 

 immersed in an oil-of-vitriol bath, the heat of which could be 

 regulated at pleasure. By means of a perforated cork, an in- 

 chned condensing-tube, about a foot long, was next attached. 

 This was narrowed at the further extremity, so as to enter a 

 small receiver, from which a tubulus, in its turn, carried the 

 gaseous products of the reaction into a vessel containing lime. 



Materials. — Details respecting individual nitrates will be 

 alluded to more especially hereafter. However carefully pre- 



