ON ARTIFICIAL REFRIGERATION. 023 



or twice, and you will obtain a washing wliich contains no ammonia ; it 

 is only superlicial." 



Liquid ammonia (liquor ammonise), or the aqueous solution of ammonia 

 of commerce contains varyin;;- quantities of ammonia in water, a(.'cor(lin<^ 

 to temperature. A mean usually stated is that water dissolves TOO vol- 

 umes of the gas. At 0° C, 0.875 gramme or 1,148 cubic centimeters of 

 ammonia gafe are absorbed by one gramme of water under normal x)ressure. 

 The avidity of the combination is attended with the evolution of heat, 

 and this fact is demonstrated by passing a ciu'rent of air through a cold . 

 concentrated solution of ammonia, displacing the gas, which carries off 

 the heat of the intruded air, and the li(iuid falls below —40°, so that by 

 this method mercury may be frozen. 



At ordinary temperatures, ammonia is a transparent gas, alkaline in 

 reaction, colorless unless the air contains a little hydiochloric acid, when 

 visible white fumes ai^pear. Its tension at different temperatures varies 

 greatly. 



The volumes of ammonia gas at different temperatures are, according 

 to Andreefl', as follows : 



Temperatm-e 10° C. 0° C. -f 10° C. + 20° C. 



Volume 0.09805 1.000 1.0215 1.0450 



The coefficient of expansion between —11° and O^C. is, according to the 

 mean of three observations by Joll}', 0.00155 ; so that at temperatures 

 sufficiently removed from its boiling-x)oint ammonia exx)ands more than 

 a gas. 



At —38.5, according to Eegnault, or at —35^.7, according to Loir and 

 Drion, ammonia is liquid at atmosx^heric pressure. By a mixture of 

 chloride of calcium and ice Guyton de Morveau condensed ammonia into 

 aliquid at — 52°C., andBunsenat — 40°C. Guyton de Morveau's original 

 exx)eriment, in which he liquefied ammonia at —21° C, shows the influence 

 of an admixture of water in changing the x>i'Oxierties of ammonia, an 

 influence which Ch. Tellier had discovered when he recommended and 

 Xjateuted the liquefaction by x^ressure of anhydrous ammonia in ice- 

 machines. 



The sx)ecific gravity of the liquefied anhydrous ammonia is 0.70, and 

 it is a colorless, very mobile liquid, refracting light more powerfully than 

 water. 



Faraday solidified it at —103° Fahr., when its vax)or tension was stiU 5 

 pounds to the square inch. 



The pressures and temx^eratiu'es at which ammonia gas, dried by chlo- 

 ride of calcium or fused caustic x^otash, could alone be liquefied, led to the 

 idea, until Tellier dispelled it, that for the x)urposes of artificial refrigera- 

 tion it could only be used with water. Prof. F. A. P. Barnard, of l^ew 

 York, one of the commissioners at the Paris Universal Exx^osition of 

 1807, wrote in the rex^ort I have elsewhere quoted a very clear and def- 

 inite statement of the Aiews then entertained. M. Tellier's x^atent was 

 in the secret archives of the French ijatent-ofiice, and Indeed the diffi- 



