VOL. LXXVIII.] fMlLOSOPHICAL TRANSACTIONS. 403 



shoot, as soon as they can be made to do so, by putting in a small bit ' of ice or 

 snow; for thus the fallacy which might otherwise arise from the deposition of 

 some of the salt will be avoided. A doubt having been suggested, whether the 

 contact of a crystal of salt might not also bring on the congelation, that experi- 

 ment was tried, but it produced no effect. Indeed, the formation of saline crys- 

 tals in these experiments, the liquor still remaining fluid, was a sufficient proof 

 to the contrary. On the whole it seems evident from the preceding table, that 

 the effect of nitre, like that of common salt, is to depress the freezing point in 

 the simple ratio of its proportion to the water; which will be found universally 

 true when allowance is made for the deposition and other sources of fallacy before 

 enumerated. This nitre produced, with snow, a cold of between 26° and 1^^, 



Sal Ammoniac, 

 As nitre sunk the freezing point of water so little, namely, but 6°, Dr. B. had 

 recQurse for the next set of experiments to that neutral salt which, after sea salt, 

 produces the greatest cold with ice; which is, the common sal ammoniac. The 

 different solutions of this salt in water, being submitted to the action of the 

 frigorific mixtures, froze according to the following table. 



The third column is calculated from the last ex- 

 periment but one, in which the freezing point 

 of a solution of 1 part of the sal ammoniac in 

 5 of water proved to be 8°. In this table also 

 the numbers of the 3d column agree sufficiently 

 with those of the id to show, that sal ammo- 

 niac, like the 2 preceding salts, depresses the 

 freezing point in the simple ratio of the propor- 

 tion in which it is mixed with the water. 

 It has been a question much contested, whether saline solutions deposit their 

 salt on freezing. That some separation, or a tendency to separation, takes place, 

 many facts concur to prove; and among the rest some phenomena observed in 

 the above-mentioned experiments; For instance, the stellated crystals, when 

 first formed, were barely suspended in the water, and sometimes they even gra- 

 dually subsided to the bottom ; which shows, that they consisted of salt chiefly, 

 only inviscated with ice, or at at least of an over proportion of salt: for the prin- 

 cipal mass of ice formed in a saturated solution floats in it like common ice in 

 pure water. Sometimes in solutions of sal ammoniac, and such other salts as 

 separate by the cooling of the water, a sort of flocculent substance is formed, 

 which subsides in the water, and is thus distinguished from the proper ice of the 

 solution, which it otherwise much resembles in appearance. It is composed 

 chiefly of the deposited salt, in very minute crystals like powder, inviscated and 

 kept together with a little ice. The sal ammoniac, mixed with snow, produced 

 a cold of from 4° to 4-^° of Fahrenheit's scale. 



