282 PHILOSOPHICAL TRANSACTIONS. [aNNO l/S/. 



degrees. One remarkable circumstance occurred to Mr. Walker, as he was 

 endeavouring to ascertain the best strength of the vitriolic acid: he happened to 

 be trying a mixture of 2 parts of oil of vitriol and one of >yater, when he ob- 

 served that, at the temperature of 35°, the mixture coagulated as if frozen, 

 and the thermometer became stationary; but, on adding more Glauber's salt, it 

 fell again, after some little time, but so great a cold was not produced as when 

 this circumstance did not occur, and when the acid was weaker. The same 

 appearance of congelation took place with other proportions of acid and water, 

 at other temperatures. 



Mineral alkali, when it retained its water of crystallization, added to some of 

 these mixtures heightened their effects. But when it had lost this water, it 

 rather produced heat than cold; and the same thing is also true of Glauber's 

 salt. This circumstance leads us, in some measure, to the theory of these phe- 

 nomena. Water undoubtedly exists in a solid state in crystals; it must there- 

 fore, as in other cases, absorb a determinate quantity of fire, before it can 

 return to its liquid state. On this depends the difference between Glauber's salt 

 and fossil alkali in their different states of crystallization and efflorescence. The 

 same circumstance too enables us to understand the great effect of Glauber's salt, 

 which, as far as I recollect, has the greatest quantity of water of crystallization. 

 Those therefore who shall chuse to pursue the path which Mr. Walker has 

 opened to them, would do well to try combinations of salts containing much 

 water of crystallization; but they must take care lest the effect should be dimi- 

 nished or destroyed by the formation of compounds that fix a smaller quantity of 

 fire. It is however but justice to Mr. Walker to observe, that he has carried 

 his experiments in this way very far, and with great ingenuity. 



XXVII. An Account of a Douhler of Electricity, or a Machine hy tvhich the 

 least conceivable Quantity of Positive or Negative Electricity may be Con- 

 tinually Doubled, till it becomes Perceptible by Common Electrometers, or 

 Visible in Sparks, By the Rev. Abraham Bennet, M. A. p. 288. 



This paper, with improvements, may be consulted in the author's electrical 

 papers, collected and printed at Derby in 1789. 



XX Fill. Some Particulars relative to the Production of Borax. In a Letter 

 from fVilliam Blane, Esq., to Gilbert Blane, M. D., F. R. S. Dated Luck- 

 now, Aug. 28, i78d. p. 297. 



My journey to the northern mountains in Jan. last, says Mr. B., in atten- 

 dance on the Vizier, gave me an opportunity of satisfying, in some degree, my 

 curiosity on the subject you are so desirous of being informed of, the production 

 and manufacture of borax. The place which his excellency visited is called 



