178 ANNUAL OF SCIENTIFIC DISCOVERY. 



ILLUSTRATION OF THE DEVELOPMENT OF HEAT BY SOLIDIFICA- 

 TION, ETC. 



In most chemical text-books, no good examples are given of the develop- 

 ment of heat by mere solidification. It is, indeed, usually mentioned, that 

 water may be cooled many degrees below the fieezing-po:nt, and remain 

 liquid; and that on congealing, its temperature suddenly rises to ^'2" F. But 

 the experiment is so troublesome to make, especially in the lecture-room, that 

 these truths commonly pass us matters of faith rather than of sight, and the 

 important principles which they illustrate, often fail of being distinctly im- 

 pressed on the mind of the student. Now, many of the hydrated salts, and 

 among them the nitrates, melt at points above the common temperature of 

 the air, and are therefore well adapted for showing, at all seasons, and wiih 

 great case and clearness, the inertia of bodies with regard to change of form 

 and the liberation of sensible heat by crystallization.* Nitrate of lime is pre- 

 eminently suitable for the exhibition of these properties, since, after having 

 been fused and heated above loCP F., it may be cooled in a glass vessel as 

 low as 60, and kept in the liquid state a long time, often for several days ; 

 but on dropping in a bit of solid nitrate, crystallization immediately com- 

 mences, and an inserted thermometer soon rises to 11 (P F. 



A substance which may be had both liquid and solid at a temperature 

 considerably below the melting-point, is obviously A'ery convenient for dis- 

 playing the comparative densities and specific heats in the two forms, as 

 complications caused by differences of temperature, may be entirely avoided. 

 Thus, the specific gravity of a specimen of nitrate of lime in the liquid state, 

 at 00 F., was found to be 1'79. Some of the same was poured into oil of 

 turpentine, made to solidify, and cooled to 00 F. Its density was now 1'DO. 

 The contraction may be rendered appreciable by the eye, if we cool to a cer- 

 tain degree some melted nitrate contained in a long-necked flask, nil with an 

 oil up to a marked height, effect the crystallization, and then cool to the 

 same point as before. 



To illustrate the absorption of heat during the liquefaction of solids, freez- 

 ing mixtures are commonly employed, in which one of the ingredients, ice, 

 is already cold. The experiment is more striking, when all the articles used 

 are at the temperature of the surrounding air. Such may be the case if we 

 take crystallized sulphate of soda and a sesquinitrate. A mixture of thirty- 

 six grams of powdered pernirrate of iron crystals, and fifty-seven grams of 

 fine Glauber's salt, liquefied and lowered the thermometer from 65 F. to zero. 

 It readily froze water contained in a test-tube. In cold weather, eight grams 

 of the nitrate and 9'5 grams of the sulphate, brought the thermometer from 

 2'2 to 10. J. M. Ordway, Sillimans Journal, Jan. 18-39. 



ON THE MELTING AND SOLIDIFICATION OF TVATER. 



M. Mousson reports, in the Bibliotheque Universelle de Geneve, an interest- 

 ing set of experiments, made by him for the purpose of determining the 

 effect of pressure on the melting-point of ice. 



* In an excellent work published in 1857, "Lehrbuch cler physikalischen und 

 theoretischen Chemie, von H. Buff, II. Kopp und F. Zamminer,"- - hyposulphite 

 of soda is mentioned as capable of affording a very striking example of the liL-at 

 becoming free during fixation; but this salt is less easy to prepare than most of the 

 nitrates. 



