1874.] On the Chemical Constitution of Saline Solutions. 241 



the thermometer is put in motion, and immediately the tube has acquired 

 a slightly oblique position, the mercury breaks off at the point D, runs 

 into the curved and enlarged portion E, and eventually falls into the 

 tube F, when this tube resumes its original perpendicular 'position. 



The contrivance for turning the thermometer over may be described as 

 a short length of wood or metal having attached to it a small rudder or 

 fan ; this fan is placed on a pivot in connexion with a second, and on 

 this second pivot is fixed the thermometer. The fan or rudder points up- 

 wards in its descent through the water, and necessarily reverses its posi- 

 tion in ascending. This simple motion or half turn of the rudder gives 

 a whole turn to the thermometer, and has been found very effective. 



Various other methods may be used for turning the thermometer, 

 such as a simple pulley with a weight which might be released on touching 

 the bottom, or a small vertical propeller which would revolve in passing 

 through the water. 



March 19, 1874. 

 JOSEPH DALTON HOOKER, C.B., President, in the Chair. 



The Eight Hon. Viscount Cardwell was admitted into the Society. 

 The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : 



I. " Preliminary Notice of Experiments concerning the Chemical 

 Constitution of Saline Solutions." By WALTER NOEL HARTLEY, 

 F.C.S., Demonstrator of Chemistry, King's College, London. 

 Communicated by Professor STOKES, Sec. R.S. Received 

 February 3, 1874. 



The author has been engaged in investigating the above subject during 

 the last eighteen months, and his experiments being still in progress, he 

 thinks it desirable to place the following observations on record. 



In the examination of the absorption-spectra, as seen in wedge-shaped 

 cells, of the principal salts of cerium, cobalt, copper, chromium, didymium, 

 nickel, palladium, and uranium, to the number of nearly sixty different 

 solutions, it was noticed that the properties of the substances in regard 

 to changes of colour could be ascertained by noticing the absorption- 

 curves and bands, so that, provided water be without chemical action, 

 it could be foreseen what change would occur on dilution of a saturated 

 solution. 



The effect of Heat on Absorption-spectra. 

 When saturated solutions of coloured salts are heated to 100 C., 1st, 



