AND RATIO OK TIIKIK ATOMUJ WKKillTS. 47 



Date. Hour. Weight, gr. 



May i8 4.30 p.m. 41.8173 



May 18 5.40 P.M. 41.8155 



May 19 2.30 P.M. 41.8159 



May 19 7.30 P.M. 41.8159 



May 20 1 1. 00 A.M. 41.8159 



Obviously tlie first weigliiiig was iiuule too soon. Tlie nicaii of tiie otlicr 

 weighings is 41.8158 gr. 



The \\eio-hina' after the first washiuaj shows the well-known loss of material 

 produced by the solvent action of watei- after glass has l)een exposed for a long 

 time to the decomposing effect of the air. The next weighing shows that a second 

 washing soon after the first may have a much less solvent action ; that of May 

 15 shows that gentle friction with powdered pumice may not remove anything from 

 a surface already well washed. 



If it were safe to argue from the increase from 41.8168 to 41.8175 gr. we might 

 perhaps infer that repeatedly wiping the second globe was gradually producing a 

 loss such as the first suffered from the first washing; but the inference is too 

 insecure. 



28_ OXYGKN ]5Y SECOND METHOD. PREVENTING LEAKAGE OF GLOBES WHEN EXHAUSTED. 



Since, with a balance of such gratifying constancy, but a few repetitions of a 

 weighing were necessary, it would have pei-haps been safe to trust the stopcocks 

 which had been fused to the globes. But since the manipulation which entirely 

 prevents the leakage of the stopcocks when the globe is exhausted is by no means 

 difiicult, it was always used in this series of determinations. 



Fig. 20. — Method of preventing leakage of globes when exhausted. 



At y, Fig. 2<», is the ground joint of the stopcock l)y which the globe is 

 always connected to other apparatus. The piece h r/, which fits on <j was reduced to 

 a small diameter at c (the tube at c should have been drawn as at d) and a mark 

 was etched here; the piece was then put in position on the stopcock, and the 

 volume contained between this mark and the key of the stopcock was determined 

 by filling from a burette. This was done once foi- all. When the globe was to be 

 exhausted, this joint was fused to the joint d e, and dra^vn to a small diameter at d, 

 ready to be closed by fusion when exhausted, and tlie volume between the mark c and 

 the point d was determined by filling it with water and weighing. The two joints 

 having been thus made ready, h was warmed and coated internally with wax ready 

 for cementing on y. Then the two joints with this wax were carefully weighed by 



