INDUSTRIAL PROGRESS DURING THE YEAR 187G. ly 



tween these numbers obtained in a good vacimm and those of 

 Graham and Maxwell at ordinary pressures, proves that this coeffi- 

 cient is independent of pressure. The coefficient of conductibility 

 was determined from the time which a thermometer placed in the 

 gas required to cool. At a certain limit of pressure the influence of 

 convection disappeared, the cooling being due solely to radiation 

 and conduction. By obtaining the most complete vacuum possible, 

 they saw the rapidity of cooling become independent of the form of 

 the vessel, and hence the conductibility is nil. In this way they 

 showed the conductibility of hydrogen to be 7.1 times that of air, 

 while that of carbon dioxide is 0.59. A curious fact observed was 

 that the rapidity of cooling is by far the best test of the i^erfectiou 

 of a vacuum. 



Duclaux has observed and investigated the curious fact that a 

 homogeneous liquid mixture may, by a change of temperature or by 

 certain additions, become separated into two layers. For instance, 

 a mixture of 15 cubic centimeters of amyl alcohol, 20 cubic centim- 

 eters of ordinary alcohol, and 32.9 cubic centimeters of water is 

 homogeneous above 20 ; but the least lowering of temperature be- 

 low this, even by one tenth of a degree, causes the division of the 

 liquid into two nearly equal layers. The author proposes to use 

 this fact in the construction of an exceedingly delicate minimum 

 thermometer. Convenient volumes of amyl and ethyl alcohols are 

 mixed together, brought to the required temperature, and water 

 gradually added, drop by drop, till a slight turbidity results. The 

 liquid is then sealed in a tube, being first colored with carmine. 

 Whenever the temperature falls below that at which it was pre- 

 pared, the two layers appear, and of diflerent tints. If methyl al- 

 cohol and ether be thus used, a maximum thermometer may thus be 

 made. 



Berthelot has given a system of classification of acids and bases 

 founded on the decomposition of their salts by water, as shown by 

 the thermal changes which result. In the first class are placed 

 strong acids and bases. These, wdien separately dissolved in water 

 and mixed in equal equivalents, produce an amount of heat whicli 

 is nearly constant for all, and which is not increased by a new ad- 

 dition of water or of the base. Such salts, then, are not decomposed 

 by water. The second class includes feeble acids. These form salts, 

 even with strong bases, which are decomposable by water, the de- 

 composition progressively increasing with the amount of water add- 

 ed. With some of the bodies of this class, however, the progress of 

 the decomposition is gradual either up to a certain limit or indefi- 

 nitely, while with others it is effected totally upon the first addition 

 of the water. In the first class are placed chlorides, nitrates, and 

 neutral sulphates of the fixed alkalies; in the second, the borates, 

 carbonates, cyanides, sulphides, alkali-phenates, acetates, butyrates, 



