552 Intelligence and Miscellaneous Articles. 



I am now extending this inquiry to pressures exceeding that of 

 the atmosphere, and hope soon to lay before the Society the detailed 

 results of the whole series, together with some observations on the 

 causes of this variation of luminosity. 



" On the Porism of the In-and-circumscribed Polygon." By Arthur 

 Cayley, Esq., F.R.S. 



" On a New Auxiliary Equation in the Theory of Equations of the 

 Fifth Order." By Arthur Cayley, Esq., F.R.S. 



LXXI. Intelligence and Miscellaneous Articles. 



NOTE ON THE FREEZING OP SALINE SOLUTIONS. 

 BY M. RUDORFF. 



ABATER which contains saline substances in solution, freezes, as 

 * * is well known, at a considerably lower temperature than pure 

 water, and in passing into the solid state carries with it only a very 

 small proportion of the dissolved salts. M. Rudorff proposed 

 to investigate as large a number as possible of saline solutions, in 

 reference to these two phenomena, and to ascertain if they were 

 not subject to definite laws. 



By experiments with solutions of common salt, of sulphate of 

 copper, and of bichromate of potash, he first ascertained that the pro- 

 portion of salt in the ice formed is always far less than that in the 

 mother-liquor. The lamellar structure of the ice led him even to 

 think that the salt which it contained was merely mechanically 

 mixed, and that the ice, properly so called, was quite pure. 



He then proceeded to a determination of the exact tempera- 

 tures at which ice forms in different solutions. He prepared, with 

 each of the salts, a series of solutions containing respectively 

 1, 2, 3 ... . parts of salt to 100 of water. He placed each of 

 them successively in a mixture of snow and salt, and stirred it witli 

 a thermometer which indicated twentieths of a degree Centigrade, 

 until it solidified. Under these conditions, the freezing was sudden, 

 simultaneous throughout all the mass, and accompanied by a marked 

 increase of temperature. After this first determination (which was 

 not entirely accurate, in consequence of the change in the composi- 

 tion of the liquor resulting from the instantaneous formation of a 

 large quantity of ice) M. Rudorff made a second experiment, in 

 which, without stirring the solution, he cooled it to about half a 

 degree below the temperature at which the liquid froze in the pre- 

 ceding experiment. He then projected a few flakes of snow into 

 the liquid, and observed that congelation took place accompanied by 

 a slight increase of temperature, and he took the last indication of 

 the thermometer for the freezing-point of the solution investigated. 

 The formation of ice then continued for a long time without 

 change of temperature ; and it was only after a considerable quan- 

 tity of ice had been formed that cooling commenced. If the solu- 

 tion was then taken out of the freezing-mixture and placed in a 



