On a veil- Mod-j cf Arl\ficial Ccrgrl^tlon. 421 



It is obvious, therefore, that the refrigerating powers cculd be 

 p'l'ihed still further bv a judicious combination of the apparatus. 

 It would be easy to show, that the maximum effect is obtained, 

 when the tlirneusions of the successive cases rise in a geometn- 

 ck\ pro-ressinu. The action, however, is not doubled for eacu 

 additional case, but increased rather more than one-half. 



Simpler Mode of Congelalion, hij dry pounded IF/dnstone, or 

 parched Oatmeal. 



These plans are difficult in the execution; and though they en- 

 large our conceptions of the extent of the descending scale ol 

 heat, yet they furnish merely speculative results. A very inv- 

 portant practical improvement has been lately made in the pro- 

 cess of artificial congelation. Sulj.huric acid is certainly a cheap 

 end most powerful agent of absorj-tion ; but the danger in using 

 v.ich a corrosive liquid, especially by unskilful persons, formed 

 always a serious obstacle to its general adoption. Mr. Leslie 

 I'.ad early noticed the remarkable absorbent quality of our mould- 

 ering w'hinstone or porphyritic trap; and in April 1817 tie 

 substituted that material, grossly pounded and dried before a 

 kitchen fire, instead of sulphuric acid, and actually froze a bcdy 

 of water with great facility. This earth will attract the fift;eth 

 part of its weight of moisture before its absorbent power is re- 

 iluced to the one-half, and is hence capable of freezing the sixth 

 part of its weight of water. It may be repeatedly dried, and 

 will, after each operation, act with thesaime energy as at first. 



But an absorbent still more convenient and powerful has since 

 occurred to Mr. Leslie; — it is merely parched oatmeal. With 

 ?. body of oatmeal of a foot in diameter, and rather more than 

 an inch deep, he froze a pound and a (juarter of water, con- 

 tained in a hemispherical porous cup. The meal h easily dried 

 and restored again to its action. In a hot climate, the exposure 

 ".o the sun alone might prove sufficient. By the help of th;s 

 •imple material, therefore, ice will be easily and safely produced 

 in any climate, and even at sea. 



Other substances could, no doubt, be employed as absorbents. 

 But, except the muriate of lime, or what is called the oil of salt 

 fieticcated, none hold out any prospect of success. Dried com- 

 mon salt will barely effect congelation ;, and stucco, or the sul- 

 phate of lime, deprived of its water of crystallization, which 

 Jii'ght seem to promise a powerful absorption, has scarcely any 

 cif-:ccy v,hatever. 



D d 3 LX.\I. On 



