4-04 Mr. Walker on the artificial Production of Cold. 



prepared cream is to be frozen : this cavity, forming a circle 

 within the vessel itself, is open at the top, as represented, and of 

 course closed at the bottom, and reaching very nearly (as the 

 tube in fig. 1.) to the bottom of the vessel : this secondary part, 

 as likewise represented, fits close as in fig. 1. over the vessel 

 containing the freezing mixture. The proportions of the appa- 

 ratus when together are thus : The outer space in width, two 

 parts all round ; the middle space, or that which contains the 

 cream, one part all round ; and the inner space three parts in 

 width, — this serving as a general scale of proportions for an 

 apparatus of any size. The proportions for an efficient appa- 

 ratus, as my own, may be : for the first space ten-eighths of an 

 inch (one inch and one-fourth); for the second, five-eighths of 

 an inch ; and for the third space, fifteen-eighths, or rather two 

 inches, making the width of the apparatus itself somewhat above 

 five inches and a half; its height being equal to its width, a 

 projecting rim at the bottom likewise to insulate it from the 

 table. It will be perceived that in the figure there are seven 

 very small holes or apertures in the central part of this cover 

 (one in the centre and six round at due distances), just suffi- 

 cient for the escape of the air, to admit of the ascent of the 

 freezing mixture in the middle part of the vessel. This ap- 

 paratus is somewhat elevated at the top, or slightly convex, 

 and the part in which the apertures are placed guarded by a 

 shallow rim to prevent an accidental running-over of the mix- 

 ture into the part containing the cream. This apparatus should 

 be furnished (as expressed in the figure) with an outer cover 

 similar, but less elevated, to the one at fig. 2. Previously to 

 use it will be proper to ascertain the quantity of liquid the ap- 

 paratus will contain when together, and mark its height ; like- 

 wise the proportion of the ingredients for furnishing a given 

 quantity in measure should be known. Thus, if the three salts 

 are used (which I would recommend to a private individual, 

 always doing so myself, although these cannot be recovered 

 for future use, but being more efficacious than the two only) 

 for each pint, small or old measure, will be required of sal am- 

 moniac and nitre (each equal parts by weight reduced together 

 into fine powder) six ounces, and of Glauber's salt, in clear 

 crystals and dry, four ounces and a half, freely reduced to 

 fine powder, or kept from the access of air, and in a separate 

 parcel from the former ; and water ten ounces, or enough to 

 make up one pint in measure when added to the former in- 

 gredients :— of course, the whole must be well stirred together, 

 and expeditiously, before introducing that part of the apparatus 

 which contains the article to be frozen, and occasionally after- 

 wards, till the object is completed, avoiding as much as possi- 

 ble 



