348 Mr. E. J. Mills on the Chemical Activity of Nitrates. [May 19, 



Two series of experiments were then most carefully made, at pressures 

 equal to depths of 250, 500, 750, &c. to 2500 fathoms, the results of 

 which satisfactorily proved that the strongest-made unprotected thermo- 

 meters were liable to considerable error, and therefore that all previous 

 observations made with such instruments were incorrect. 



Experiments were also made in the testing-apparatus with Sir Wm. 

 Thomson's enclosed thermometers, to ascertain the calorific effect pro- 

 duced by the sudden compression of water, in order to find what error, if 

 any, was due to compression in the Miller pattern : an error was proved 

 to exist, but small, amounting to no more than 1° # 4 under a pressure of 

 3 tons to the square inch. 



The dredging cruize of the 1 Porcupine' afforded an opportunity of com- 

 paring the results of the experiments made in the hydraulic testing-appa- 

 ratus, with actual observation in the ocean, and a most careful series of 

 observations were obtained by Staff-Commander E. K. Calver at depths 

 corresponding to the pressure applied in the testing-apparatus ; the result 

 was that, although there was a difference in the curves drawn from the 

 two modes of observation, still the general effect was the same, and the 

 means of the two were identical. 



From these experiments and observations a scale has been made by 

 which observations made by thermometers of similar construction to those 

 with unprotected bulbs can be corrected and utilized, while it is proposed 

 that by means of observations made with the Miller pattern in the posi- 

 tions and at the same depths at which observations have been made with 

 instruments not now procurable for actual 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 unsatisfactory 

 working of the steel .indices, which, from mechanical difficulties in their 

 construction, cannot always be depended on, two instruments should be 

 sent down for every observation ; and although their occasional disagree- 

 ment 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. 



IV. "On the Chemical Activity of Nitrates." By Edmund J. 

 Mills, D.Sc. Communicated by Prof. A. W. Williamson. 

 Keceivcd April 21, 1870. 



(Abstract.) 



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 word?, to trace the modifications undergone 



