451 



must, therefore, then think the vapour as removed. It is clear that 

 the weighed quantities must then be corrected for the quantity of 

 substance which is found in the vapour phase at the vanishing 

 point. For this, volume and pressure of the vapour must be known. 

 In the observation of the vanishing point the position of the meniscus 

 was for this purpose indicated on the tube by means of a writing- 

 diamond. The volume of the vapour, which practically consists 

 of water here, as the vapour pressure of NH^Cl is negligible at 

 all the observed temperatures, was then measured after the tube 

 had been cut open, with water from a burette. The pressure could 

 be read from table I and then the quantity of water in the vapour 

 could be calculated by the aid of the laws of Boyle and GayLüss.\c. 

 On account of the deviation from I he gas-laws this cahnilation is of 

 course not quite accurate, but the correction being small, this method 

 of determination is, after all, acciu'ate enough for this purpose. It 

 is, of course, necessary to lake the vapour space as small as possible. 

 First the tubes were filled with ammonium chloride and weighed ; 

 then from a burette, a definite quantity of distilled water was 

 added and brought into the tube through the capillary connecting 

 tube and stem by repeated heating and cooling. The tube (of com- 

 bustion glass) was then fused to in the lighting gas oxygen flame, 

 and weighed again. The determinations marked by crosses in table 2, 

 were carried out in tubes of from 25 to 30 grams; these were 

 weighed down to half milligrams. In later determinations the weight 

 of the tubes of about 15 grams was determined down to tenths of 

 milligrams. As the weighing of the tubes can easily give rise to 

 errors on account of the large surface, I think that less value is to 

 be attached to the determinations marked with crosses than to the 

 others. In the second and third columns of table 2 the weighed 

 quantity of substance is given; the fourth column gives the observed 

 vanishing points, which were determined in an oilbath, electrically 

 heated by 220 Volts of alternate current, which was regulated by the 

 insertion of incandescent lamps. Uniformity of temperature in the 

 oilbath was ensured by rapid stirring. The fifth column gives the 

 quantities of water in the vapour at the vanishing point calculated 

 according to the above given method ; the sixth column contains the 

 corrected quantity of water ; the seventh the quantity of grams of 

 NH^Cl to 100 grams of water in the liquid saturate with gas and 

 solid substance. Finally the eighth column gi\es the value for — log x, 

 in which x represents the number of molecules of NH^Cl present in 

 one mol. of the mixture. Hence x is given by : 



