PHYSICS. 455 



this liquid by a quantitj" nearly constant, which is not far from O.C3o. 

 (J. Phys., January, 1884, II, in, IC.) 



Guthrie has given the name eutcxia to the property iiossessed by cer- 

 tain compound badies of fusing at very low temperatures, such bodies 

 being called eutectic bodies or eutectics. He uses the term for bodies 

 made up of two or more constituents, which constituents are in such 

 proportion to one another as to give the resulting comi)ound body a 

 minimum temperature of liquefaction. Taking up metallic alloys, he 

 finds that the eutectic alloy of bismuth with lead contains 44.42 of 

 lead and fuses at 122.7°; with tin, 53.90 per cent, of tin and fuses at 

 133^; with cadmium, 40.81 per cent. Cd, melting at 144°; and with zinc, 

 7.15 per cent, of zinc, fusing at 248°. A tetra-eutectic alloy, containing 

 47.38 of bismuth, 19.36 of lead, 13.29 cadmium, and 19.97 of tin, fused 

 at 71°, below the temperature of boiling alcohol. His next experiments 

 were made with salt alloys. With niter, fusing at 320°, the eutectic 

 alloy with potassium sulphate fused at 300°, with potassium chroraate at 

 295°, with barium nitrate at 278, with strontium nitrate at 258°, with 

 calcium nitrate at 251°, and with lead nitrate at 207°. The analogy 

 between eutectic alloys of this sort and cryohydrates is pointed out, and 

 the geological and mineralogical importance of eutexia is discussed in 

 the original paper. {Phil. Mag.., June, 1884,V, xvii, 462 ; Nature, June, 

 1884, XXX, 139.) 



Trouton has compared together the quantities of heat necessary to 

 evaporate at constant pressure quantities of different liquids taken ib 

 the ratio of their molecular weights, and finds that the amount of heat 

 required by any body is approximately proportional to its absolute 

 tem})erature at the point of ebullition. By multiplying the latent heat 

 by the density, the amount of heat required to evaporate a quantity of 

 a body proportional to its molecular weight is obtained ; and the ratio 

 of this value to the absolute temperature of the boiling point is approxi- 

 mately constant. Thus, the latent heat of bromine is 45.9, it boils at 



63° and its density is 79.75. Hence, i^^ill^-'^ = 10.89. The la- 

 ' "^ '273 + 63 



tent heat of butyric acid is 114.7, it boils at 162°, and its density is 44. 



114 7 X 44 

 Hence,-;-=^^ — -^^y = 11.59, a nearly identical value. The author con 



eludes that the molecules of bodies, and especially of chemically related 

 ones, in changing from the gaseous to the liquid state at the same press 

 ure, disengage quantities of heat which may be called the molecular 

 latent heat, directly proportional to the absolute temperature of the 

 boiling point. {Phil. Mag.., July, 1884, V, xviii, 54.) 



Klobakow has devised an instrument for determining the vapor den 

 sity of bodies of high and of low boiling points, respectively*. For lov^ 

 boiling points the apparatus (which he calls a vapor-density dilato 

 meter) resembles a weight thermometer. For bodies of high boiling 

 point 1 e uses an apparatus resembling an araometer, consisting of a 



