TRAMSACTldNS OF THK SECTtONS. 61 



From these examples the cause of the evolution of heat is evident, 

 and we have a method of determining the absolute quantity of heat in 

 bodies, which has been so long a desideratum. 



On a Method of Ascertaining the Strength of Spirits. By Wm. Black. 



The author believes it has long been a desideratum with Government 

 to find a more scientific and accurate mode of trying the strength of 

 spirits than that now in use. A very slight inattention in the mode of 

 using the hydrometer may malte a difference of at least five per cent. ; 

 and when the spirits are adulterated with sugar or salts that instrument 

 is totally useless. 



It is generally known that when equal quantities of proof spirits and 

 water are mixed together at equal temperatures between 50° and 60° 

 Fahrenheit, the thermometer will, if immediately immersed in the 

 mixture, rise 91 degrees, half a degree of caloric being perhaps ab- 

 sorbed by the instrument in making the experiment. 



Mr. Black however thinks it is not so generally known that the 

 thermometer rises more or less according to the strength of the spirits, 

 and that it does so apparently in very regular progression. When spi- 

 rits 45 per cent, over proof are mixed in equal quantities with water, 

 both being at the same temperature, between 50° and 60°, the thermo- 

 meter, if immediately immersed in the mixture, will rise 14 degrees ; 

 but with the strongest alcohol, also mixed in equal quantities with 

 water, it will not rise above that temperature unless more water be add- 

 ed, showing that no further concentration takes place, and that the al- 

 cohol can only combine with the water in fixed proportions, and that a 

 certain portion of the spirit must remain in the first mixture in an un- 

 combined state. Every degree on the thermometer appears to indicate 

 a diflference of 10 per cent, in the strength of the spirit. Thus, if we 

 mix equal quantities of spirit, 10 per cent, over proof, and water, both 

 at equal temperatures of about 55°, the thermometer will rise 10|°; 

 with spirits 20 o.p. it will rise 11^°; and so on, one degree for every 

 additional 10 per cent. o. p. until it reaches 40 or 45 o.p., when no 

 further increase is apparent, unless, as before stated, more water be 

 added. 



The thermometer seems to act in a similar manner with spirits under 

 proof; thus with spirits 10 per cent. u. p. mixed with water as above 

 the indication is 8|°, and one degree less for every 10 per cent, under 

 until we get to 45 per cent, tj.p., after which, although a rise does take 

 place, Mr. Black is not sure that the indications are so regular. 



When spirits are mixed with sugar, thus increasing the specific gra- 

 vity so as to falsify the hydrometer 20 or 30 per cent or more, the in- 

 dications of the thermometer are precisely the same, if we make al- 

 lowance for the slight difference in volume caused by the mixture of 

 sugar. 



If the mixtures be made at higher temperatures the thermometer indi- 

 cates a lesser number of degrees in rise according to the temperatures. 



