490 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 67. 



scarcely 2 oz. of spirit of salt distilled into the bottle, fig. c. The receiver and 

 bottle c seemed cold to the touch; the water at f had increased 2 lb. 3 oz. 

 Another like bottle, with the same quantity of water, being put in the room of 

 this, in some time acquired the same degree of heat. The fumes seem to 

 condense very well until the water acquired a heat within 12 degrees of boiling 

 water. Spirit of wine rectified, made use of instead of water to condense the 

 vapours, acquires a heat equal to 188 degrees; and it becomes of a deep brown 

 colour, though transparent. 



Oil of turpentine applied to the same use, acquires a heat of 12 degrees above 

 that of boiling water, or 224 degrees; it becomes of a dark brown colour, 

 though transparent, and has a disagreeable bituminous smell. The ther- 

 mometer not measuring more than 213 degrees, could not be left in with safety 

 any longer. Another time oil of turpentine was made use of to condense the 

 vapours, which proceeded from lib. -i- of sal ammoniac, with lib. -i- of oil of 

 vitriol, and -|- of a pound of water: here it did not get near so hot, nor so 

 high coloured, as in the experiment, but was for the most part congealed. 

 The difference of these two experiments may, perhaps, be owing to the small- 

 ness of the quantity of the ingredients in the last process; for in the first, 

 there was 14 lb. of salt, 14lb. of vitriol, and 7 lb. of water. 



Of the re-absorption of air in distillations. — In all distillations a quantity of 

 elastic air is set free in the beginning; but afterwards there is a re-absorption 

 of the same; the following experiment was made to show how great it is 

 in some cases. For the apparatus, see fig 1 . 



One poundand a half of foreign sal ammoniac was put into a retort, and 1 lb. and^ 

 of oil of vitriol (previously diluted the day before with -f of a pound of water) 

 poured on it, and a recipient well luted to it; the recipient had a tube 31 inches, 

 well fitted and luted to it; and this tube was immersed in a glass vessel contain- 

 ing a quart of water. 



The spirit of salt which was distilled, weighed 1 lb. 2 oz. 5 dr. 



The quart of water increased in weight 3 4 



The caput mortuum weighed 2 3 4 



The loss in the operation was only 3 



3 12 O 



The operation was continued till the sal ammoniac began to sublime. 



When no more air escaped, which might easily be perceived by its ceasing to 

 bubble through the water, the vessel of water was taken away, and the tube 

 was immersed in a basin of quicksilver; the mercury rose in the tube 23 inches 

 and a half, while the recipient was too hot to bear one's hand on it longer than 

 half a minute; when the recipient was quite cold, tlie mercury rose to 29 inches 

 and T^y, and there was near one inch of spirit of salt on its surface. This 



