On a vew Mode of Arlificial Congelation, 419 



tnsy be connected with the same machine. If we suppose but 

 six of these to be used, the labour of a quarter of an hour will 

 set as many evaporating pans in full action, and may, therefore, 

 in less than an hour afterwards produce nearly six pounds of 

 solid ice. The waste which the water sustains during this con- 

 version is e'xtremelysmall, seldom indeed amounting to the fiftieth 

 part of the whole. Nor, till after multiplied repetitions, is the 

 action of the suipiuuic acid considerably enfeebled by its aqueous 

 absorption- At first that diminution is hardly perceptible, not 

 being tlie hundredth part when the acid has acquired as much as 

 the tenth of its weight of water. But such influence gains ra- 

 pidly, and rises with accelerated progression. When the quan- 

 tity of moisture absorbed amounts to the fourth part by weight 

 of the acid, the power of supporting cold is diminished by a 

 twentieth ; and, after the weights of both these come to be 

 equal, the refrigerating energy is reduced to less than the half. 

 Sulphuric acid is hence capable of effecting the congelation of 

 more than twenty times its weight of water, before it has im- 

 bibed near an equal bulk of that liquid, or has lost about the 

 eighth part of its refrigerating power. The acid should then be 

 removed, and concentrated anew by slow distillation. 



Congelation might be connected with the Steam- Engine. 

 When the exhaling and absorbing surfaces are rightly disposed 

 and apportioned, the moderate rarefaction, from twenty to forty 

 times, which is adequate to the freezing of water, may be readily 

 procured by the condensation of steam. In all manufactures 

 where the steam-engine is employed, ice may, therefore, at all 

 times be formed in any quantity, and with very little additional 

 expense. It is only required to bring a narrow pipe from the 

 condensing vessel, and to direct it along a range of receivers, 

 under each of which the water and the acid are severally placed. 

 These receivers, with which the pipe communicates by distinct 

 apertures, may, for the sake of oeconomy, be constructed of 

 cast-iron, and adapted with hinges to the rim of a broad shal- 

 low dish of the same metal, but lined with lead to hold the acid. 



Congelation of Mercury. 



The combined powers of rarefaction and absorption are capa^ 

 ble of generating much greater effects than the mere freezing of 

 water. Such frigorific energy, however, is at all times sufficient 

 for effecting the congelation of mercury. Accordingly, if mer- 

 cury, contained in a hollow pear-shaped piece of ice, be sus- 

 pended by cross threads near a broad surface of sulphuric acid 

 under a receiver; on urging the rarefaction, it will become frozen, 

 and may remain in that solid state for the space of several hours. 



D d 2 But 



