PHYSICS. 351 



meters long, and having in its interior a bar of steel and one of zinc, 

 also forming a thermometer. Irregularities in the results of comparisons 

 of two bars in the same tube led to an examination of the question 

 whether a zinc bar has always the same length at a given temperature. 

 The comparisons were made with great care, and every precaution taken 

 to avoid error. The results showed that the zinc bar of the standard 

 meter, heated for 20 hours or more to a temperature of 70° F., and then 

 allowed to cool to its original temperature, 36° F., has a certain length; 

 that if it is then cooled for 20 hours to a temperature of — 3° F., and 

 afterward is allowed to return gradually to its original temperature of 

 36° F., it has a certain other length; and that these lengths at the 

 same temperature may differ by 15 microns (thousandths of a millimeter). 

 The four-meter zinc bar heated from 41° to 75° F., and then cooled to 

 43° F., was increased in length about 29 microns, or 7 microns per 

 meter for a change of 30° F. {Am. J. Sci., Ill, July, 1881, xxii, 26.) 



Miss Walton has studied, in the Massachusetts Institute of Technol- 

 ogy, the phenomena of liquefaction and cold produced by the mutual 

 reaction of solid substances. With reference to liquefaction, the follow- 

 ing conclusions are drawn: (1) as a rule one of the substances should 

 behydrated; (2) moistening sometimes take place when salts arc mixed 

 with acids, or with bases, and when acids and bases are mixed, as well 

 as salts; (3) as with liquids, if metathesis can result, it will take place 

 with liquefaction ; (4) if an insoluble compound is formed on mixing two 

 salts, a mixture of two others, like the new ones formed, will not in gen- 

 eral be attended with liquefaction; (5) if no insoluble compound is formed 

 metathesis is partial, and it is often indifferent whether two salts be 

 mixed or their products of interchange ; (0) the rule in liquids in regard 

 to weak and strong acids and bases seems to prevail with solids also; 

 (7) when oxidation or reduction can take place there is possibility of 

 liquefaction. On the production of cold the author accepts Ordway's 

 view, that the liquefaction of salt by ice is due to the diffusion which 

 goes on between them, analogous to that between liquids. The mixtures 

 were made in a calorimeter, and the results showed that the minimum 

 temperature is not independent of the initial temperature, and that, 

 moreover, this minimum varies with the proportions taken. The lowest 

 temperature was given by mixing equivalent weights of manganous 

 nitrate and sodium carbonate at — 2° C, the temperature falling to 

 —26° C. {Am. J. Sci., September, 1881, III, xxii, 206.) 



Hagenbach has experimented on the rupturing effects of the freezing 

 of water. During the severe cold at Bale on the nights of the 10th and 

 11th December, 1879, and the 20th and 2lst January, 1880, he filled 

 artillery shells with water and observed the phenomena which took 

 place. The shells were burst, and the ice, afforded free passage, showed 

 a filamentary structure, like suddenly congealed jets of water. The 

 water, suffused within the shell, was cooled to a low temperature without 



