Fbbeuary 23, 1900.] 



SCIENCE. 



287 



oxygen and hydrogen should be measured 

 with the gases contained in vessels of the 

 dimensions of those used for obtaining their 

 densities. 



If these syntheses and these studies of 

 ratios of densities and combining volumes 

 should agree as well as it is safe to expect, 

 we should know the atomic weight of oxy- 

 gen as confidently as we can know it while 

 the value rests on a single chemical process, 

 the combination of the two gases to form 

 water. 



But this is not so much as is desirable. 

 We know the atomic ratio between silver 

 and oxygen with considerable confidence, 

 because this rests not on a single chemical 

 process but on eight different chemical proc- 

 esses, which give eight independent results, 

 and because these eight resvilts agree. Is 

 there, then, any chemical process by which 

 the atomic ratio of oxygen and hydrogen 

 can be determined, other than the analysis 

 or synthesis of water? Is there any ele- 

 ment whose atomic ratio to oxygen is well 

 known, whose ratio to hydrogen is capable 

 of accurate direct determination ? 



It is probable that, given an adequate 

 equipment, the direct ratio of hydrogen to 

 chlorine, of hj^drogen to sodium, of hy- 

 drogen to magnesium, or of hydrogen to 

 aluminum, could be determined with suffi- 

 cient precision for the purpose, provided 

 that the ratio of chlorine to oxygen, of 

 sodium to oxygen, of magnesium to oxygen, 

 and of aluminum to oxygen are well enough 

 known. This may 'not now be the case 

 with aluminum or magnesium, but is the 

 case with chlorine and with sodium, whose 

 atomic ratios to oxygen may be fairly as- 

 sumed to be known within 1 part in 2500. 

 If, now, we can determine the ratio of 

 chlorine to hydrogen, or of sodium to 

 hydrogen, to 1 part in 5000, we could com- 

 pute, by a new method, the ratio between 

 hydrogen and oxygen. If this should agree 

 with the present value, within some such 



quantity as 1 part in 2000, we should be 

 as confident of the truth of our value of the 

 atomic weight of oxygen as we can well 

 hope to be. 



The difficulties in making a complete syn- 

 thesis of hydrochloric acid are not small, 

 nor are they all well understood. Some 

 unexpected circumstance may be prohibi- 

 tive. But there is good reason to hope that 

 .3 or 4 or 5 grams of hydrogen could be 

 weighed, that a nearly equivalent quantity 

 of chlorine could also be weighed, that the 

 two could be combined, and that the prod- 

 uct could be weighed. One serious diffi- 

 culty would be found in attempting to pre- 

 pare pure chlorine, but the difficulty does 

 not seem insuperable. The manipulation 

 of the corrosive element requires invention, 

 but seems not difficult. For the collection 

 of the hydrochloric acid in a weighable 

 form, thei'e seem to be alternative methods, 

 not very troublesome of execution, unless 

 unforeseen difficulties are encountered. If 

 the ratio between hydrogen and chlorine 

 could be determined to 1 part in 5000 or to 

 1 part in 10,000, it would be a very inter- 

 esting addition to our list of known con- 

 stants, most helpful in establishing confi- 

 dence in the ratio between oxygen and 

 hydrogen. 



So, also, if sodium can be prepared of 

 sufficient purity, or of sufficiently constant 

 impurity, it seems possible to weigh 100 or 

 200 grams, to act on with water in such a 

 way as to produce a slow evolution of hy- 

 drogen, and to determine the weight of this 

 hydrogen by loss. Whether sodium can be 

 obtained sufficiently free from absorbed hy- 

 drogen and whether it can be prepared for 

 weighing without attacking the vessels which 

 contain it, are questions which need further 

 experiment. It is probable that a vessel of 

 platinum-iridium alloy could be made which 

 would make success almost certain, but at 

 considerable cost. In this case also, if the 

 ratio between sodium and hydrogen can be 



