Intelligence and Miscellaneous Articles. 465 



nations of the amount occluded in the dust by direct heating, and 

 also by combustion with cupric oxide. I likewise made the sugges- 

 tion that the hydrogen, in the cases both of the dust and the meteor- 

 ite, had probably been originally derived from water, and not neces- 

 sarily, in the latter case, from the meteorite having at one time 

 been exposed to an atmosphere of hydrogen at a high pressure. 

 The present paper is to be regarded as a study of the effect of 

 water, in the forms of liquid and vapour, upon the amount of 

 hydrogen occluded. As my later determinations were made on a 

 fresh specimen of the commercial dust, I considered it necessary, 

 in the first place, to determine the volume of the hydrogen con- 

 tained in it. In the course of the experiments it was found, on 

 leaving the apparatus to repose after the hydrogen had been ex- 

 pelled, that the volume of the mixture of gas and air in the 

 measuring-tube gradually diminished ; and this is one cause of 

 the variations in the amounts obtained in the earlier experiments. 

 Variations in the volumes are also caused by differences in the tem- 

 peratures to which the retorts containing the zinc dust are exposed ; 

 and, at an early stage of the experiments detailed in this paper, I 

 was led to finally abandon the use of soft glass in favour of retorts 

 made from combustion-tubing. 



Determination of the Hydrogen contained in a Fresh Sample of 

 the Zinc Dust, 



Experiment 1. — 6*4790 grammes of a fresh sample of zinc dust 

 were heated in a soft glass retort to as high a temperature as it 

 would bear. The arrangements were precisely the same as in the 

 experiments detailed in my second paper. The reason why I con- 

 tinued to use 6-4790 grammes (100 grains) was because this amount 

 had been previously found to occupy the volume of one cubic cen- 

 tim. All volumes are reduced to a temperature of 60° Fahr. (15°*55 

 C.) and a pressure of 30 inches of mercury ; and a correction is 

 made for the volume of that portion of the exit tube of the retort 

 which enters the measuring-apparatus. The graduated tube before 

 the experiment contained 46*8 cubic centim. of air. After the 

 apparatus had cooled to the atmospheric temperature, the volume 

 was found to be 78 cubic centim. This gives 31*2 cubic centim. 

 for the hydrogen expelled from 1 cubic centim. of the zinc dust 

 at the temperature at which the experiment was made. This is 

 the lowest result yet obtained, and was doubtless due to insufficient 

 heating. 



Experiment II. — In this experiment 6-4790 grammes were 

 heated in a horizontal retort made from hard combustion-tubing. 

 The air in the measuring-tube before heating amounted to 7*3 cubic 

 centim. After heating and subsequent cooling to atmospheric 

 temperature the volume was 44*1 cubic centim. ; after deducting 

 the air we have 36*8 cubic centim. from 1 cubic centim. of zinc 

 dust. This result approximates pretty closely to the experiment 

 in my second paper, which gave 37*5 cubic centim. 



Experiment III. — In this experiment the utmost heat of the lamp 

 was continued for a long time — until, in fact, there was no indica- 



