April 13, 1893] 



NATURE 



569 



the globe are carried to such a point that the weight of the 

 residual gas may be neglected, thus eliminating errors due to a 

 second manometer reading. There is no difficulty in attaining 

 this result, but the delicacy of the Tcippler employed as a gauge 

 is so great that the residual gas still admits of tolerably acjurate 

 measurement. Now in exhausting the head of the manometer 

 it would be easy to carry the process to a point much in excess 

 of what is necessary in the ca-e of the globe, but there js evi- 

 dently no advantage in so doing. The best results will be 

 obtained by carrying both exhaustions to the same degree of 

 perfection, 



The Water Contents of the Globe. 



The globe being packed in finely-divided ice, was filled with 

 boiled distilled water up to the level of the top of the channel 

 through the plug of the tap, that is, being itself at 0°, was filled 

 with water also at o°. Ttim charged the globe had now to be 

 weighed ; but this was a matter of some difficulty, owing to 

 the very small capacity available above the tap. At about 9° 

 there would be a risk of overflow. Of course the water could 

 be retained by the addition of extra tubing, but this was a com- 

 plication that it was desired to avoid. In February, 1882, 

 during a frost, an opportunity was found to effect the weighing 

 in a cold cellar at a temperature ranging from 4° to 7°. The 

 weights required (on the same side of the balance as the globe 

 and its supports) amounted to 0*1822 gram. On the other side 

 were other weights whose values did not require to be kn^wn 

 so long as they remained unmoved during the whole series of 

 operations. Barometer (corrected) 758*9 mm. ; temperature 6° 3. 



A few days later the globe was discharged, dried, and re- 

 placed in the balance with tap open. 1834*1701 grams had 

 now to be associated with it in order to obtain equilibrium. The 

 difference, 



1834*170—0*182=1833*988, 



represents the weight of the water less that of the air displaced 

 by it. 



It remains to estimate the actual weight of the air displaced 

 by the water under the above mentioned atmospheric conditions. 

 It appears that, on this account, we are to add 2*314, thus 

 obtaining 



1836*30 



as the weight of the water at 0° which fills the globe at o''. 



A further small correction is required to take account of the 

 fact that the usual standard density is that of water at 4° and 

 not at 0°. According to Broch (Everett's "C.G.S. System of 

 Units "), the factor required is 099988, so that we have 



1836*30 

 0*99988 



1836*52 



as the weight of water at 4° which would fill the globe at 0°. 



Air. 



Air drawn from outside (in the country) was passed through 

 a solution of potash. On leaving the regulating tap it traversed 

 tubes filled with fragments of potash, and a long length of 

 phosphoric anhydride, followed by a filter of glass wool. The 

 arrangements beyond the regulating tap were the same for all 

 the gases experimented upon. 



In deducing the weight of the gas we compare each weighing 

 " full " with the mean of the preceding and following weights 

 "empty," except in the case of October 15, when there was no 

 subsequent weighing empty. The results are 



Mean 



2*37661 



There is here no evidence of the variation in the density of air 

 suspected by Regnault and v. Jolly. 



To allow for the contraction of the globe (No. 14) when 

 weighed empty, discussed in my former papers, we are to 



add 0*00056 to the apparent weight, so that the result for air 

 becomes 



2*37717. 



This is the weight of the contents at 0° and under the pressure 

 defined by the manometer gauge at 15° of the thermometer. 

 The reduction to standard conditions is, for the present, post- 

 poned. 



Oxygen. 



This gas has been prepared by three distinct methods : (a) 

 from chlorates, {b) from permanganate of potash, {c) by 

 electrolysis. 



In the first method mixed chlorates of potash and soda were 

 employed, as recommended by Shenstone, the advantage lying 

 in the readier fusibility. Two sets of five fillings were effected 

 with this oxygen. In the first set (May, 1892) the highest result 

 was 2*6272, and the lowest 2*6266, mean 2*62691. In the 

 second set (Juie, July, 1892) the highest result was 2*6273 and 

 the lowest 26267, mean 2 62693. 



The second method {b) proved very convenient, the evolution 

 of gas being under much better control than in the case of 

 chlorates. The recrystallised salt was heated in a Florence 

 flask, the warhout, in this case also, being facilitated by a 

 vacuum. Three fillings gave satisfactory results, the highest 

 being 26273, the lowest 26270, and the mean 2-62714. The 

 gas was quite free from smell. 



By the third method I have not as many results as I could 

 have wished, operations having been interrupted by the break- 

 age of the electrolytic generator. This was, however, of less 

 importance, as I had evidence from former work that there is 

 no material difference between the oxygen from chlorates and 

 that obtained by electrolysis. The gas was passed over hot 

 copper, as detailed in previous papers. The result of one filling, 

 with the apparatus as here described, was 26271. To this may 

 be added the result of two fillings obtained at an earlier stage of 

 the work, when the head of the manometer was exhausted by an 

 independent Sprengel pump, instead of by the Toppler. The 

 value then obtained was 2*6272. The results stand thus : — 



Electrolysis (2), May, 1892 



(I) 

 Chlorates (5), May, 1892 

 (5), June, 1892 

 Permanganate (3), January, 1893 



Mean ... 



Correction for contraction 



2 6272 

 2-6271 

 2 6269 

 2 6269 

 2*6271 



262704 

 0*00056 



2*62760 



NO. 1224, VOL. 47] 



It will be seen that the agreement between the different 

 methods is very good, the differences, such as they are, having 

 all the appearance of being accidental. Oxygen prepared by 

 electrolysis is perhaps most in danger of being light (from con- 

 tamination with hydrogen), and that from chlorates of being 

 abnormally heavy. 



Nitrogen. 



This gas was prepared, in the usual manner, from air by 

 removal of oxygen with heated copper. Precautions are re- 

 quired, in the hrst place, to secure a sufficient action of the 

 reduced copper, and secondly, as was shown by v. Jolly, and 

 later by Leduc, to avoid contamination with hydrogen which 

 may be liberated from the copper. I have followed the plan, 

 recommended by v. Jolly, of causing the gas to pass finally over 

 a length of unreduced copper. The arrangements were as 

 follows : — 



Air drawn through solution of potash was deprived of its 

 oxygen by reduced copper, contained in a tube of hard glass 

 heated by a large flame. It then traversed a (J-tube, in which 

 was deposited most of the water of combustion. The gas, prac- 

 tically free, as the event proved, from oxygen, was passed, as a 

 further precaution, over a length of copper heated in a com- 

 bustion furnace, then through strong sulphuric acid,' and afiei- 

 wards back through the furnace over a length of oxide of copper. 

 It then passed on to the regulating tap, and thence through the 

 remainder of the apparatus, as already described. In no case 



1 There was no need for this, but the acid was in position for another 

 purpose. 



