410 Mr. Charles T. Heycoch [April 2, 



determining the freezing point of tlie alloy we find that it is lowered 

 in direct proportion to the weight of gold added, notwithstanding the 

 fact that pure gold by itself melts at a temperature of 1060° C. It is 

 remarkable that the effect of increasing the quantity of gold in the 

 alloy continues to depress the freezing point of the sodium, until the 

 alloy contains more than 20 per cent, of gold when the minimum 

 freezing temperature 81 '9° C (eutectic temperature) is reached. The 

 case of gold dissolving in sodium may be taken as a very general one, 

 for a large number of pairs of metals have been examined, and with 

 but few exceptions, such as antimony dissolved in bismuth, the effect 

 is almost always to produce a lowering of the freezing point of the 

 solvent metal. By the solvent metal we generally mean the metal 

 which is present in the largest quantity. 



A second point in which metallic alloys resemble ordinary 

 solutions is in the fact that the depression of the freezing point 

 is inversely proportional to the molecular weight of the dissolved 

 substance. Thus, if we dissolve 34:2 grams (molecular weight in 

 grams) of cane sugar in 10 litres of water, and determine the freezing 

 point of the solution, it is found to be depressed a definite number of 

 degrees below that of pure water. But the same depression of the 

 freezing point is ju'oduced by the solution of 126 grams of crystallised 

 oxalic acid, or only 32 grams of formic acid, in 10 litres of water.* 

 Alloys again appear to obey the same law ; thus it is found that if 

 we dissolve 197 grams of gold, or 112 grams of cadmium, or 39 

 grams of potassium, respectively, in a constant weight of sodium, the 

 freezing point of the sodium will be lowered by almost the same 

 number of degrees in each case. Now the numbers 197, 112 and 39 

 are the atomic weights of the metals, and it can be shown that these 

 numbers are also probably the molecular weights of these elements. 

 Hence we conclude that metals dissolved in each other obey the 

 same laws as ordinary solutions. 



The above facts for the behaviour of solutions of substances in 

 water and organic liquids have been gradually accumulated by the 

 work of Blagden, Eiidorff, Coppet and Eaoult, extending from about 

 1780 to the present time, but no general explanation of them was 

 brought forward until Van'tHoff advanced the remarkable theory 

 that a dissolved substance was in a condition somewhat analogous to 

 that of a gas, the solvent substance serving the part of the vessel in 

 which the gas is confined, but also exerting other effects. 



He further gave strong reasons for believing that substances in 

 dilute solution obeyed the same laws that gases do — i.e. the laws 

 of Boyle and Charles for temperature and pressure. Several other 

 theories of solution, besides what may be termed the gaseous theory, 



* Although water is used as a solvent by way of illustration in these cases, it 

 should be stated that it is by no means a suitable liquid for such experiments, 

 owing to the changes it brings about in the substances dissolved. In making 

 such experiments it is far preferable to use benzene or acetic as a solvent. 



