HEAT OR CALORIC. 87 



Distillation in vacuo, although it is attended by no economy of 

 heat, is a good mode of conducting the process, where the product 

 would be injured by a high temperature. 



Vinegar as commonly distilled, has often an empyreumatic taste, 

 but if distilled in vacuo, it requires only 130 of heat, and the pro- 

 duct is pellucid and fine. L. u. K. 



In these cases, the vacuum is obtained either by driving out the 

 air by the vapor, and then closing the aperture of the receiving ves- 

 sel, or, by applying a syringe or air pump to the receiver, cold being 

 also of course in all cases applied to the receiver.* 



(i.) The specific heat of the vapors of different fluids is different, 

 and can be ascertained by experiment only. 



Table of latent heat of vapors.^ 



Despretz, Ann. de 



Ure's Die. 17. Chim. &c. xxiv. 329. 

 Vapor of Water, at 212 1000. 955.8 



Alcohol, sp. gr. 0.825, 457. (sp. gr. .793, 



Sul. ether, boiling point 104, 312.9 ( " " .715, 

 Spt. turpentine, " about 310, 183.8 (" " .872, 



373.86 

 163.44 

 138.24 



Petroleum, 183.8 



Nitric acid, (sp. gr. 1 .494- boiled at 165,) 550. 



Liquid ammonia, (sp. gr. 0.978,) 865.09 



Vinegar, (sp. gr. 1.007,) 905. 



The force of vapor at the boiling point is the same in all fluids ; 

 it is equal to 30 inches of mercury, and in all fluids, is the same for 



* In consequence of a tax laid by the English parliament on the Scotch stills, by 

 wffich they were to pay thirty shillings a year on every gallon of the capacity of 

 their stills, it became their interest to make them work as fast as possible, and they 

 made such improvements in the construction of their stills, that, although the tax 

 was augmented by degrees from thirty shillings a year on a gallon, to fifty four 

 pounds, they still continued to carry on the business with advantage. The improve- 

 ments consisted chiefly iu making the still very broad and very flat, so that only a small 

 depth of wash could be In it at once, leaving a very large orifice for the escape of the 

 vapor, having an internal moving apparatus for agitating the wash, to prevent its 

 burning, and another in the upper part of the still to break the frothy effervescence, 

 when it would be in danger of boiling over. The fire was applied to a very large 

 surface ; the ebullition was very rapid and general ; no pressure was opposed to the 

 escape of the vapor, and thus they arrived at such astonishing rapidity in the distilla- 

 tion, as to run off their stills of forty or fifty gallons capacity, three times in an hour, 

 or seventy two times in twenty four hours, (see report on the Scotch Distillery, Phil. 

 Mag. Vol. VI. pa. 76,) and by improvements still subsequent, they brought the pro- 

 cess to such perfection, that a still of the capacity of forty gallons in the body, and 

 three in the head, charged with sixteen gallons of wash, could be worked four hun- 

 dred and eighty times in twenty four hours, viz. seven thousand six hundred and 

 eighty gallons of wash could be distilled, and as the wash would afford eighteen per 

 cent of spirit, it follows, that one thousand, three hundred and eighty two gallons 

 could be distilled from a still of this capacity in twenty four hours, the still could be 

 worked off therefore, twenty times in an hour, or once in three minute;?, and gave 

 about fifty eight gallons an hour, or near a gallon in a minute. 



* Quoted from Henry, 10th London edit. Vol. I. p. 125. 



