VOL. LXXVII.3 PHILOSOPHICAL TRANSACTIONS. 2/9 



gation, whether there is not some analogy between the congelation of the smoking 

 oil of vitriol, and the very curious crystallization which Dr. Priestley observed in 

 a concentrated vitriolic acid, saturated with nitrous acid vapours*; and whether 

 this smoking quality does not proceed from some marine or other volatile acid, 

 which may be contained in the martial vitriol, whence the vitriolic acid is ob- 

 tained. 



XXVJ. Of some New Experiments on the Production of Artificial Coid.-jf By 

 Thomas Beddoes, M. D. Dated Oxford^ May 2, 1787. p. 282. 



Mr. Walker, apothecary to the RadclifFe Infirmary, has been engaged up- 

 wards of a year in a series of experiments on the means of producing artificial 

 cold, several of which seem to be very remarkable, and such as, considering 

 their novelty, and the attention which has lately been paid to this subject, I 

 flatter myself, says Dr. B., will be found to deserve a place among the Trans- ' 

 actions of the r. s. Mr. Walker, in his first experiments, found, as Boerhaave had 

 done before him, that sal ammoniac, as well as nitre, well dried in a crucible, 

 and reduced to a fine powder, will produce a greater degree of cold than if they 

 had not received this treatment. But Boerhaave, by sal ammoniac, lowered the 

 temperature of water only by 28°; whereas Mr. Walker observed his thermo- 

 meter to fall 32°, and when he used nitre 1 9°. It occurred to him, that the 

 combination of these substances would produce a greater effect than either sepa- 

 rately: and he found that this was really the case. A proposal for freezing 

 water in summer, mentioned by Dr. Watson (Essays 3, 1 39) determined him 

 to attempt the same thing in this way. Accordingly, April 28, 1786, the ther- 

 mometer standing at 47°, he made a solution of a powder, consisting of equal 

 parts of sal ammoniac and nitre, in a basin, by means of which he cooled some 

 water, contained in a glass tumbler, to 22°. To this he added some of the 

 same powder, and immersed 2 very small phials in it; one containing boiled, the 

 other unboiled water; when he soon found the water in the phials to be frozen, 

 the unboiled freezing first. 



Having observed that Glauber's salt, when it retains its water of crystallization, 

 produces cold during its solution, he thought of adding this to his other powers, 

 and July 18, 1786, reduced the thermometer 46°. In this experiment the fol- 



* Experiments and Observations relating to various Branches of Natural Philosophy, vol. i. p. 25 

 and 450. M. Cornette has also effected the crystallization of vitriolic acid by distilling it with nitrous 

 acid and charcoal. Memoir, de I'Acad. des Scienc. Paris, pour 1779'— Orig. 



+ See a further account of these experiments by Mr. Walker in the 78th, 79th, 86th, and 93d 

 vols, of the Phil Trans. The greatest degree of artificial cold was produced without pounded ice 

 or snow, by a mixture of 9 parts phosphate of soda, 6' parts nitrate of ammonia, and 4 parts diluted 

 nitric acid. With pounded ice or snow, the greatest degrees of cold were produced by mixing 3 parts 

 jnuriate of lime with 1 part snow 5 or by adding 10 parts diluted sulphuric add to 8 parts snow. 



