On the Detached Colorimeter. 437 



dT 



the differential coefficient -=-; and in that case the potential 



energy T of the liquid does change ; consequently the retard- 

 ing force in question above is not augmented then, as in the 

 general case ; and for this reason the diameter of the sheet 

 must be greater than usual. 



This curious result of my theory is fully confirmed by Sa- 

 vart's experiments. With an orifice of 3 millims. the aureoled 

 open sheet had a diameter of 20 centims. when the water was 

 at 1°*3 C. and was impelled by the pressure of 4*885 metres ; 

 while the sheet under the same pressure, but at the tempera- 

 ture of 4° C.j had a diameter of 36 centims. — that is to say, 

 nearly four times the surface. In my opinion, this consider- 

 able difference simply proceeds from the potential energy T of 

 the water at its maximum of density having a maximum value, 



so that — - = 0. 

 dt 



(e) If the foregoing conclusion is accurate, in operating 

 with water at 10° C, for example, a cooling must be found to 

 take place in the sheet, while, on the contrary, if the water is 

 at first at, say, 1 0, 3, it must grow warmer in spreading. 



(/) Since, as I have proved in a previous investigation, to 

 every thermal variation a difference of electric potential cor- 

 responds, the spreading-out of water at its maximum of density 

 into a sheet cannot give rise to a thermoelectric current, pro- 

 vided the temperature in it does not change ; on the contrary, 

 the formation of the liquid sheet must be accompanied by a 

 current in one direction if the initial temperature of the liquid 

 be above 4°*5, and in the opposite direction if it be below 4°*5. 



I purpose soon to control this important consequence of my 

 formula. If direct observation verify it, I shall therein find 

 a. brilliant confirmation of the theory I am seeking to introduce 

 into science. 



LXVII. On the Detached Colorimeter, and on Colorimetry. 

 By Edmund J. Mills, D.Sc, F.R.S., "Young" Professor 

 of Technical Chemistry in Anderson s College, Glasgow*. 



THE ordinary detached colorimeter consists of two equal 

 test-tubes mounted on feet. It is a simple, but in many 

 respects an imperfect, instrument. Several of its defects were 

 removed by the Portable Colorimeter f , which has been found 

 to work well in the majority of cases. Room, however, has 



* Communicated by the Author. 



t Proc. Phil. Soc. Glasgow, x. p. 310. 



