NATURAL PHILOSOPHY. 101 



using ammonia as the agent, 10 horse-power working 10 hours 

 has the cooling power of one ton of ice, and one ton of coal, or 

 a week's supply, has the virtue of 14 tons of ice. Tlie professor 

 finds an excellent evaporation in condensed gas from petroleum 

 wells or stills. This gas can be condensed into fluid by very 

 little pressure, and boils at a temperature of 30° Fahrenheit. 



Curious Production of Cold. — Dr. Phipson has recently dis- 

 covered that an intense degree of cold is produced by dissolving 

 sulphocyanate of ammonium in water. Many salts, more es- 

 pecially salts of ammonia, lower the temperature of water while 

 dissolving ; but, according to Dr. Phipson, no compound pro- 

 duces this effect in so marvellous a manner as sulphocyanate of 

 ammonium. In one experiment 35 grammes of this salt dis- 

 solved rapidly in 35 cubic centimetres of water at 23° Cent., 

 caused the thermometer to descend in a few seconds to 10° Cent. 

 The moisture of tlie atmosphere instantly condensed itself on the 

 outside of the glass in thin plates of ice. — Scientific Review. 



As a general rule, according to experiments by M. ISchultz, it 

 has been found that the point of solidification of fluids is lowered 

 by substances dissolved therein, and that gases dissolved in fluids 

 exercise the same effects. Pure acetic acid fuses at 16° ; this is 

 lowered to 15.2° when a current of carbonic acid is transmitted 

 through this acid. It is well known that hydrochloric acid gas 

 and ammonia gas lower the freezing temperature of water in 

 which they are dissolved ; so do carbonic acid and sulphurous acid 

 gas; and it has been ascertained by M. Schultz that nitrogen, 

 oxygen, and hydrogen gases exert the same effect when dis- 

 solved in water. Numerous experiments were made by him 

 with the view of ascertaining the effect of an increase of pressure 

 brought to bear upon the absorption of various gases by water, 

 and the lowering of the freezing-point of that liquid in conse- 

 quence thereof. By the phenomenon of regelation is understood 

 that property exhibited by ice of freezing together to a solid 

 mass, when pieces of that substance are pressed together at the 

 temperature of 0°. After quoting the opinions of Messrs. Fara- 

 day, Forbes, Thomson, and Helmholtz, on this subject, the 

 author says: "When we take it for granted that regelation is 

 the formation of ice from water anew, we must bear in mind 

 that only pure water, or water, at least, not saturated with air, is 

 suitable for this purpose." 



Photography — Self-prints from Nature. — At a meeting of the 

 Mass. Inst, of Technology, Mr. Thomas Griiffield exhibited illus- 

 trations of what he calls " Photographic Self-prints from Nature." 

 While on a visit to the country, having with him his pressure 

 frames and sensitive paper, it occurred to him that the colored 

 autumn leaves might produce varied effects, just as the colored 

 glasses did on the sensitive paper exposed beneath them. He 

 exhibited various groups of colored leaves taken in this way; 

 the red leaves generally cut off a very large amount of the actinic 

 rays, while the other colors passed a considerable amount; the 

 thickness of the leaves, their dryness from age, and the hardness 

 of the veins and ribs, are elements which determine the amount 



