120 On the Coefficient of Expansion of Gas- Solutions. 



The strength f Munke's solution was 13*75 per cent., 

 having a specific gravity of '9465 at 12°*5 C. The results of 

 his measurements are shown in the curve marked "Munke 

 1828 " (fig. 2). Although deduced from measurements taken 

 by a different method, it falls into its proper place among the 

 other curves in the figure. 



If we take the volumes given in Table II. or Table III. for 

 any one temperature and plot a curve, using these volumes as 

 abscissae and the corresponding percentages of gas contained 

 in the solution as ordinates, we obtain a straight line — a fact 

 which finds its interpretation in the following law, viz.: — 



When ammonia gas is absorbed in water, the increase in 

 volume of the solution for a constant temperature is directly 

 proportional to the amount of gas absorbed. 



Since for C0 2 gas the same law has been found true*, we 

 feel warranted in suspecting it to be a general one. 



The series of curves in fig. 4 show the variation in volume 

 of various ammonia-solutions between —20° C. and 100° C. 

 Given the saturation-point of the solution, the amount of gas 

 which water is capable of absorbing at all temperatures, and 

 the law just stated, the curves can be easily calculated. From 

 the point of saturation to 100° C. the loss of gas more than 

 counterbalances the expansion due to heat, and the volumes 

 decrease rapidly. 



Stated briefly, the effect of NH 3 gas in solution upon the 

 water absorbing it is as follows: — 



(1) The coefficient of expansion of the solution is increased 

 by the presence of the gas. 



(2) The increase of volume due to the absorption of a gas 

 is directly proportional to the amount of gas absorbed. 



(3) The point of maximum density of water is lowered by 

 the presence of NH 3 or C0 2 gas in solution. 



(4) The freezing-point of water is lowered by the presence 

 of the above-mentioned gases. 



These results seem to us to be opposed to the opinion com- 

 monly held by chemists, that NH 3 and C0 2 , when in aqueous 

 solution, form chemical compounds of the form NH 4 HO and 

 H 2 C0 3 . The effect of these gases upon the properties of the 

 water absorbing them shows so complete an analogy to the 

 changes occurring when salts are dissolved, that we are in- 

 clined to consider the products of gas-absorption to be true 

 solutions rather than chemical combinations. 



* Mackenzie and Nichols, article already cited. 



