' ON ARTIFICIAL REFRIGERATION. 929 



oiTr Iviiowlodii'o of ice-macliines at tlie dates tliey were respectively pub- 

 lished. In his patent, No. 747, dated March 28, 1850, Mr. Harrison 

 tells us that he employs " an air-tight apparatus of three vessels con- 

 nected by tubes ; a vacuum is to be established throughout the a^ipa- 

 ratus, the air being expelled by the vapor of ether, alcohol, liquid 

 ammonia, or other volatile liquid." Mr. Harrison, so far, adopted Mr. 

 Perkins's plan of obtaining space for his vapor, since the latter recom- 

 mended filling his machine to repletion, and then taking some, say half, 

 out to make room for vapor. It is quite clear, from the perusal of Mr. 

 Harrison's patent, that the machine was designed to freeze by evaporation 

 of ether, for the alcohol and the liquid ammonia, the latter universally 

 known as a solution of gaseous ammonia in water, would have been of 

 no avail whatever in the apparatus so well described. Indeed, the 

 words, " liquid ammonia or other volatile liquid," inserted at the begin- 

 ning of his specification, would have required the description of various 

 forms of apparatus made of different materials, for the copper would 

 have been destroyed by the liquid ammonia; and the vague expression, 

 " volatile liquid," he extends to water in his claim, and we well know 

 that had he tried water in the machine he describes, it would have been 

 inoperative. This meaningless attempt to grasp everything, without 

 knowing more than that part of his subject relating to ether, is the main 

 defect of this important contribution to industrial art. He goes on to say : 

 " The nature of my invention consists in producing cold, bj'' the evap- 

 oration of a liquid in one vessel, the withdrawal of the vapor formed, 

 and the getting rid of heat thus withdrawn by the condensation of 

 the vapor in another vessel." ..." The evaporating-vessel may be 

 of tinned copper, or any air-tight an(l water-tight material of good heat- 

 conducting i)ower, capable of resisting the atmospheric pressure, and 

 not acted upon by the substances in (jontact with it, and of any shape, 

 provided there be a sufficient surface of contact respectively to the 

 liquid to l)e evaporated and the substance to be cooled. In like manner, 

 the condensing-vessel may be of any material and shape, the requisites, 

 of strength, conduction of heat, resistance to chemical action, and suf- 

 ficient surface being attended to." Having described his pump, &c., 

 and referred his readers to their knowledge of heat to supply the' 

 data for x)ractical work, he enters into definite calculations bearing on 

 the use of ether. He says : " The requisite surface of the evaporating- 

 vessel may be deduced from the ascertained fact that a surface ^ 

 of 10 square feet will evaporate fully 1 i^ound of water per minute,, 

 T\ith a difference of temperatm^e of 30° ; ^\dth a less difference, a pro- 

 portionately larger surface will be reqmred. The latent heat of other 

 liquids being less than that of water, a less surface will suffice for 

 their evaporation. For instance, the latent heat of ether at, say 24P- 

 is to that of steam at 212° as 200 to 1,000, nearly; therefore only one,, 

 fifth of the surface, or one- fifth of the difference of temperature, will 

 suffice for the evaporation of ether. The same rule will apply to the 

 59 F 



