Ure's Dictionary of Chemist r if. 343 



Several newly constructed and very valuable tables will be 

 found interspersed through this" article. The following prac- 

 tical applications of the doctrines previously inculcated, will 

 aflford an example of our author's powers of popular description : 



" But tlie most splendid trophy erected to the science of caloric, is the 

 steam-engine of Watt. This illustrious philosopher, from a mistake of his 

 friend Dr. Robison, has been hitherto defrauded of a part of his claims to 

 the admiration and gratitude of mankind. The fundamental researches 

 on the constitution of steam, which formed tlie solid basis of his gigantic 

 superstructure, though they coincided perfectly with Dr. Black's results, 

 were not drawn from them. In some conversations with which this great 

 ornament and benefactor of his country honoured me, a short period before 

 his death, he described, with delightful ndiveU,ih& simple, but decisive, ex- 

 periments by which he discovered the latent heat of steam. His means 

 and his leisure not then permitting an extensive and complex apparatus, 

 he used apothecaries' phials. With these, he ascertained the two main 

 facts, first, that a cubic inch of water would form about a cubic foot of 

 ordinary steam, or 172H inches ; and that the condensation of that quantity 

 of steam would heat six cubic inches of water from the atmospheric tem- 

 perature to the boiling point. Hence he saw that six times the difference of 

 temperature, or fully 900° of heat, had been employed in giving elasticity 

 to steam ; which must be all abstracted before a complete vacuum could 

 be procured under the piston of the steam-engine. These practical deter- 

 minations he afterwards found to agree pretty nearly with the observations 

 of Dr. Black. Though Mr. AVatt was then known to the Doctor, he was 

 not on those terms of intimacy with him, which he afterwards came to be, 

 nor was he a member of his class. 



" Mr. Watt's three capital improvements, which seem to have nearly ex- 

 hausted the resources of science and art, were the following: — 1. The sepa- 

 rate condensing chest, immersed in a body of cold water, and connected, 

 merely by a slender pipe with the great cylinder, in which the impelling 

 piston moved. On opening a valve or stop-cock of communication, the elas- 

 tic steam which had floated the ponderous piston, rushed into the distant 

 chest with magical velocity, leaving an almost perfect vacuum in the cy- 

 linder, into which the piston was forced by atmospheric pressure. M'hat 

 had appeared impossible to all previous engineers vvas thus accomplished. 

 A vacuum was formed without cooling the cylinder itself. Thus it re- 

 mained boiling hot, ready the next instant to receive and maintain the elas- 

 tic steam. 2. His second grand improvement consisted in closing the cy- 

 linder at top, making the piston-rod slide through a stuffing box in the lid, 

 and causing the steam to give the impulsive pressure, instead of the atmo- 

 sphere. Henceforth the waste of heat was greatly diminished. 3. The 

 fiaal improvement was the double impulse, whereby the power of his 

 engines, which was before so great, was in a moment more than doubled. 

 The counter-weight required in the single-stroke engine, to depress the 

 pump-end of the working beam, was now laid aside. He thus freed tiie 

 madiine from a dead weight or drag (jf many hundred pounds, which had 

 hung upon it from its birth, about seventy years before. 



" The application of steam to heat apartments, is another valuable fruit 

 of these studies. Safety, cleanliness, and comfort, thus combine in giving 

 a genial warmth for every purpose of private accommodation, or public 

 manufacture. It has been ascertained, that owe cubic foot of a boiler will 

 heat about two thousand feet of space, in a cotton-mill, whose average heat 

 is from 70° to 80° Fahr. And if we allow 25 cubic feet of a boiler for a 

 horse's power in a steam-engine supplied by it, such a boiler would be 

 adequate to the warming of fifty thousand cubic feet of space. It has 

 been also ascertained that one square foot of surface of steam-pipe is ade- 

 quate to the warming of two hundred cubic feet of space. This quantity 

 U adapted to a well-finished ordinary brick or stone building. The safety 

 valve on the boiler should be loaded with two pounds and a half for an 

 area of a square inch, as is the rule for Mr. Watt's engines. Cast-iron 

 pipes are preferable to all others, for the diffusion Of heat. Freedom of 

 expansion must be allowed, which in cast-iron may be taken at about a 

 tenth of an inch for every ten feet in length. The pipes should be dis- 

 tributed within a few inches of the floor. 

 2 A2 



