Intelligence and Miscellaneous Articles. 467 



dust, on being saturated with boiling water and then dried in the 

 water-oven until the w 7 eight was constant, gave an increase of 

 00561, or 0*0363 gramme less than in the first experiment. I 

 then subjected 6*4790 grammes to a dull red heat ; and the result- 

 ing gas, in two hours after the operation, measured when all correc- 

 tions were made, gave 89 cubic centim., or 8*4 cubic centim. more 

 than in the last experiment. The two highest experiments with 

 unwetted zinc dust gave 46*4 cubic centim. and 47*4 cubic centim., 

 the mean being 46*9. The two with wetted zinc dust gave 89-4 

 and 89 cubic centim. The mean of these is 89*2, or only 4*6 cubic 

 centim. less than double the amount from unwetted zinc dust. 



It is proper to notice that the increase of weight of the zinc- 

 dust on w T etting and subsequent drying in the first experiment was 

 0*1924 gramme, and in the second 0*1561 gramme. The mean of 

 these is 0*1742. Now, if 10 atoms of zinc (65*3 x 10) had fixed 1 

 molecule of water, the increase would be 0*1785 — a number so near 

 to the mean of the experiments as probably not to be entirely with- 

 out meaning ; but, on the other hand, I have not yet had time to 

 analyze the zinc dust, which, of course, cannot be taken as repre- 

 senting even moderately pure zinc. 



Effect of Exposure of Zinc Dust to a Moist Atmosphere. 



Having shown that the wetted dust after drying gives off nearly 

 double as much hydrogen as was evolved from it in the condition 

 in which it was received, it became important to know how the 

 hydrogen had been occluded by the dust which had not been 

 wetted. It has long been known that shippers are unwilling to 

 carry large quantities of zinc dust in their vessels, owing to the 

 danger of its getting wetted, in which case it becomes heated to an 

 extent which may become dangerous. It being, therefore, extremely 

 improbable that the specimens with which I worked had ever been 

 wetted, or even rendered damp purposely, it struck me that it had 

 probably absorbed moisture from the atmosphere. This would per- 

 fectly account for the presence of hydrogen in the commercial 

 product ; and, owing to its being kept closely packed, for the 

 amount being small as compared with that contained in the dust 

 which had been thoroughly wetted. To determine the question I 

 placed 6*4790 grammes in a watch-glass over a vessel containing 

 water, the whole being th m covered by a bell-glass. The apparatus 

 was kept in a room having a nearly constant temperature of about 

 72° Pahr. It was weighed almost every day from the commence- 

 ment of the experiment (Aug. 6) un f il the 17th of September, by 

 which time it had ceased to increase. It was found that for the 

 first fourteen days it gained about 3 centigrammes a day ; the next 

 fourteen days the increase fell to about 1| centigrammes a day; 

 and after this it gradually diminished, and at last entirely ceased. 

 It was then dried in the water-oven until the weight became 

 constant. The substance which had caked together was then 

 pulverized and taken for the following experiments. 



Experiment I. — One quarter of the usual amount, namely 1*6198 

 grammes, was heated in a similar manner to the previous experi- 



