MECHANICS AND USEFUL AKTS. 63 



the mixture should assume a chocolate color. When required 

 for use it should be melted in a glue-pot ; the surface of the hoof must 

 be scraped clean, and the gutta pcrcha applied as required. The 

 application may be facilitated by the use of a glazier's knife warmed, 

 by which also the surface of the artificial hoof may be smoothed and 

 polished. In this manner many a valuable horse may be rendered 

 useful, which, otherwise, would only remain fit for slaughter. On 

 the score of humanity, also, this application of gutta percha is to be 

 welcomed. 



ARTIFICIAL MANUFACTURE OF ICE. 



The Paris Cosmos thus describes an apparatus invented by M. 

 Carre, and practically operated by him, for freezing water by means 

 of the evaporation of ammoniacal gas. 



The generator contains in its lower part, which is called the boiler, 

 190 pounds of an ammoniacal solution at 28. Under the action of the 

 heat, the ammoniacal gas is disengaged, and passes into a second com- 

 partment, which encloses a series of superposed horizontal tubes, with 

 large vertical tubulaors in the middle. This set of tubes performs the 

 function of a rectifier ; that is, the gaseous ammonia disengaged by the 

 heat conies in contact in these tubes with the liquid returning to the 

 boiler, gives up to it its vapor of water, and passes to,a state of almost 

 absolute purity. From the rectifier, the gas passes into a worm, and 

 from this to a liquefier, a collection of tubes around which is a cur- 

 rent of water, at a temperature of from 53 to 59 Fah. On coming 

 out of the liquefier, the ammonia, now liquid, and still pushed on by 

 the pressure in the boiler, which is some ten atmospheres, enters 

 another vessel called the regulator, in which floats a bell with very 

 thin metallic walls, which, by its successive risings and fallings, regu- 

 lates the discharge of the liquid, and prevents the mixture of any 

 bubbles of gas. Thus condensed, the liquid passes through the induc- 

 tion valve into the refrigerator, which is a worm wound several times 

 around the cylinders filled with the water to be frozen, which are 

 placed in a vat of an uucongealable liquid, such as a strong alcohol, 

 or, better, a sufficiently saturated solution of chloride of calcium (mu- 

 riate of lime). 



After resuming the gaseous form, at the expense of the heat of the 

 water in the cylinders, and thus freezing it, the ammonia leaves the 

 worm by a vertical tube, fills a central bottle, and comes into the ab- 

 sorber, where it comes into contact with the water exhausted of its 

 ammonia, passing from the bottom of the boiler, and minutely divided 

 by passing through a great number of small holes. There the am- 

 moniacal solution is re-formed, with a disengagement of heat, which 

 is absorbed by circulating again through cold water ; finally, from the 

 asorber, the ammoniacal solution passes into the boiler by its top, 

 and passes through the tubes of the rectifier. 



The ice forms very rapidly, and is very solid and opaque ; its tem- 

 perature is about 12 Fah., so that it is not necessary to wait until 

 the water of the cylinder freezes to the centre, as the action goes on 

 after the cylinder is withdrawn. The cylinders are removed every 

 eight minutes, and the ice of each one weighs about nine pounds. 

 With an expense of five and a half pounds of coal burned, there are 



