1870.] Mr. E. J. Mills on the Chemical Activity of Nitrates. 349 



by nitryl as it is transmitted (from the chloride, hydrate, or free radical) 

 through an adequate succession of combinations. One of the first steps 

 in this direction is the preparation of nitrylic chloride, which can be most 

 easily effected, according to a statement in Watts's * Dictionary of Che- 

 mistry' # , by the action of phosphoric oxychloride on plumbic nitrate — 



3 Pb (NO 8 ) JI +2P0 Cl 3 =Pb 3 (P0 4 ) 2 + 6 N0 2 C1. 



Among other modes of verifying this equation, the examination of 

 the residue left behind when excess of the oxychloride is heated with 

 plumbic nitrate, and then distilled off in a current of dry air, appeared the 

 most simple and obvious. The results were found not to agree with the 

 equation ; and after three nitrates had been tried, a law of chemical 

 activity became evident, rendering the reaction worthy of pursuit for its 

 own sake, although, as an available source of nitrylic chloride, it had 

 failed entirely. The nature and mode of establishment of this law con- 

 stitute the subjects of the author's memoir. 



When a nitrate is treated with phosphoric oxychloride, as has just been 

 mentioned, the residue contains phosphoric oxide and a metallic chloride. 

 Within the limits of experimental error, or subject to other satisfactory 

 explanation, the ratio between these two products is constant for each 

 nitrate ; and from that ratio a quotient a can be found as follows : — 



weight of chlorine 

 _ CI weight of chlorine 4*06 



a weight of phosphoric oxide - weight of phosphoric oxide 



PA 



This quotient, which is different for each nitrate, is termed the " co- 

 efficient of chemical activity " of nitrates, and the method of obtaining it 

 is designated the " method of ratios." The data from which a is deduced, 

 namely, certain weights of argentic chloride and magnesic pyrophos- 

 phate, are, if singly considered, new with each experiment ; they depend 

 on time, rate of heating, the state of division of the nitrate, and other con- 

 ditions. But, assuming the results to have been brought about under a 

 law of chemical action, the values of a must be independent of those cir- 

 cumstances, by which the primitive numerator and denominator could have 

 been only pari passu affected; they are related only to the actual occur- 

 rence of the reaction. This property, in a chemical ratio, has not, it is 

 believed, been previously observed. 



After describing the means employed for obtaining a current of dry air, 

 the apparatus required for the reaction, and the individual experiments 

 which were severally made, the following Table of results is given, 2 being 



V 



the symbolic value of a nitrate, and Q=-« 



* Vol. iv. p. 77. 



