160 PROCEEDINGS OF THE AMERICAN ACADEMY. 



oxide obtained from the nitrate usually contains about 0.00057 gram 

 of occluded gas ; upon this basis Morse and Burton's result would 

 become 65.458 instead of 65.2G9. 



In considering the results obtained by the second method the results 

 of Favre and Jacquelain may be rejected at once. Of Van der 

 Plaat's results it is necessary to state only that some error must have 

 crept in while recording his data, for it is inconceivable that 6.6725 

 grams of zinc should yield only 1.1424 litres of hydrogen. The 

 work of Reynolds and Ramsay was much more careful and detailed ; 

 but the results varied very widely. Hydrogen evolved from very 

 pure zinc was measured, with many precautions ; but after the 

 rejection of thirty-four experiments eleven more gave a value of 

 65.24, and still five more gave 65.47 as the atomic weight of zinc. 

 Since the publication of their work many investigations have shown 

 that the density of hydrogen is greater than the value assumed at 

 that time. If a litre of the gas weighs 0.9001 * gram, and the atomic 

 weight of hydrogen is taken as 1.0075 (O = 16.000) the atomic 

 weight of zinc deduced from Reynolds and Ramsay's experiments 

 becomes about 65.63. 



The two older results obtained by the third method are worthy of 

 no further mention. Baubigny's work upon the ignition of zincic sul- 

 phate is very interesting, but probably incomplete. It will be remem- 

 bered that the value for copper obtained by the same method was 

 too low, t owing, probably, to the occlusion of sulphuric acid by the 

 cupric sulphate. It is not impossible that a similar error may have 

 crept in here, for the conditions were similar ; but it is probable that 

 it is here counterbalanced by the retention of sulphur trioxide by the 

 zincic oxide. In a series of experiments made in this laboratory pure 

 zincic oxide obtained from the carbonate (see p. 163), was ignited to 

 constant weight in an oxidizing atmosphere at a temperature above the 

 fusing point of gold ; t it was then dissolved in dilute sulphuric acid 

 which left no residue upon evaporation, and very gradually brought 

 again to the same high temperature. In no case were we able to 

 expel all of the sulphuric acid which we had added. Three experi- 

 ments are appended : — 



* Lord Rayleigh and others. 

 t llichards, These Proceedings, XXVI. 275. 



I Four grams of pure gold melted in fifteen minutes from the time of turn- 

 ing on the air blast in tlxe furnace. 



