134 Royal Society : — 



experiment, to form a scale for correcting all observations made with 

 that particular type. 



In conclusion, it is suggested that to avoid error from the unsatis- 

 factory working of the steel indices, which, from mechanical diffi- 

 culties in their construction, cannot always be depended on, two 

 instruments should be sent down for every observation ; and although 

 their occasional disagreement of record may raise a doubt, a little 

 experience will enable the observer to detect the faulty indicator, 

 while their agreement will create confidence. 



A description of such deep-sea metallic thermometers as have 

 been invented is appended. 



" On the Chemical Activity of Nitrates." By Edmund J. Mills, 

 D.Sc. 



In the course of his researches upon nitro-compounds, the author 

 found it extremely desirable to submit the genetic relations of those 

 bodies to a detailed examination ; in other words, to trace the modifi- 

 cations undergone by nitryl as it is transmitted (from the chloride, 

 hydrate, or free radical) through an adequate succession of combi- 

 nations. 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 Chemistry' *, by the action 

 of phosphoric oxychloride on plumbic nitrate — 



3 Pb (N0 8 ) a +.2 PO 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 constitute 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 v A nc 



n — a X 4 '06. 



weight of phosphoric oxide weight of phosphoric oxide 



This quotient, which is different for each nitrate, is termed the 

 "coefficient of chemical activity" of nitrates, and the method of ob- 

 taining it is designated the " method of ratios." The data from which 



* Vol. iv. p. 77. 



