88f PHILOSOPHICAL TRANSACTIONS. [aNNO l666. 



bottles of wine or other liquors, Mr. Boyle says he did not satisfy himself by a. 

 sufficient number of trials.* 



V. For the cooling of air and liquors, and to adjust weather-glasses or ther- 

 mometers, (to be able to do which at all times of the year was one of the chief 

 aims that made me think of this experiment -}-) or to give a small quantity of 

 beer, &c. a moderate degree of coolness, it wdll not be requisite to employ near 

 so much as a whole pound of sal ammoniac at a time. A few ounces dissolved 

 in about four times their weight of water will suffice. 



VI. In this section Mr. Boyle relates, that about the end of March he w as able, 

 with a pound of sal ammoniac and a requisite proportion of water, to produce ice 

 in a very short space of time. His sealed thermoscope (containin^tinctured 

 spirit of wine) was 1 6 inches long, the ball [bulb] about the size of a walnut, 

 and the diameter of the tube about an 8th or 10th of an inch. Being put into 

 the water before the salt was added, the coloured spirit was first at 8^ inches, 

 and after some time a little beneath 7f ; but in about a quarter of an hour after 

 the sal ammoniac was added, it descended to 2-f^ inches, and in seven or eight 

 minutes before that time, the vapour and drops of water on the outside of the 

 glass began to freeze. When the frigorific power was at its height, water 

 thinly placed on the outside of the glass, whilst the mixture was quickly stirred 

 up and down, would freeze in a quarter of a minute. After three hours from 

 the beginning of the operation, the crimson liquor of the thermometer was at 

 4 4 inches, the height to which sti'ong and durable frosts had reduced it in the 

 winter. 



VII. The sal ammoniac employed in these experiments may be recovered (to 

 save expense) by evaporating the solution, and crystallizing it. The salt thus 

 obtained will serve again for fresh frigorific mixtures. J 



* As the absorption of heat or production of cold depends upon the conversion of the salt from its 

 solid form into a fluid state ; it is evident tliat, when it is only partially dissolved, as in the case of 

 its being mixing with sand and merely sprinkled with water, tlae degree of refrigeration will be very 

 inconsiderable. 



f Since Mr. Boyle's time tliermometers have been more accurately adjusted by employing snow or 

 ice just beginning to melt for the freezing point, and water boiling under a pressure of the atmosphere 

 corresponding to 29>8 of the barometer, for the boiling point. 



X A solution of sal ammoniac (muriate of ammonia) and nitre (nitrate of potash) produces a greater 

 degree of cold than a selution of sal ammoniac alone. But there are other salts which produce this 

 effect in a much stronger degree, such as tlie nitrate of ammonia dissolved in water, tlie phosphate of 

 soda dissolved in diluted nitric acid, the sulphate of soda dissolved in the same acid, or in diluted sul- 

 phuric acid, &c. See Mr. Walker's experiments on artificial cold, Phil. Trans, vols. 77, 7^- When 

 we come to give an account of tliese experiments, we shall have an opportunity of noticing the intense 

 degrees of cold which may be produced by means of snow and the diluted nitric and sulphuric 

 acids, or of snow and muriate of lime. 



