36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



First series 089938, ± .000007 



Second series 089970, ± .000011 



Preliminary series, second method 089921, ± .0000271 



Third series 089886, ± .0000049 



Fourth series 089880, ± .0000187 



Fifth series 089866, ± .0000034 



General mean 089897, ± .0000025 



Rejecting the first three 089872, ± .0000028 



This last mean value for hydrogen will be used in succeeding chapters 

 of this work for reducing volumes of the gas to weights. Combining 

 the general mean of all with, the value found for the weight of a litre 

 of oxygen, 1.42896, ±.000028, we get for the ratio H: 0, 



= 15.8955, ± .0005 



If we take only the second mean for H, excluding the first three series, 

 we have — 



O = 15.9001, ± .0005 



This value is undoubtedly nearest the truth, and is preferable to all 

 other determinations of the density ratio. Its probable error, however, 

 is given too low; for some of the oxygen weighings involved reductions 

 for temperature and pressure. These reductions involve, again, the co- 

 efficient of expansion of the gas, and its probable error should be included. 

 Since, however, that factor has been disregarded elsewhere, it would be 

 an over-refinement of calculation to include it here. Other corrections, 

 of a mathematical character, have been recently applied to Morley's data 

 by Guye and IMallet.^ They find, for the normal weight of one litre of each 

 gas, = 1.42886, and 11 = 0.089875. The difference between these fig- 

 ures and those given by Morley is so small as to be negligible. 



Still more recently, by a novel method, J. Thomsen has measured the 

 two densities in question." In his gravimetric research, already cited, 

 he ascertained the weights of hydrogen and of oxygen equivalent to a 

 unit weight of aluminum. In his later paper he describes a method of 

 measuring the corresponding volumes of both gases during the same 

 reactions. Then, having already the weights of the gases, the volume- 

 weight ratio, or density, is in each case easily computable. From 1.0171 

 to 2.3932 grammes of aluminum were used in each experiment. Omit- 

 ting details, the volume of hydrogen in litres, equivalent to one gramme 

 of the metal, is as follows : 



iCompt. Rend., 138, 1034. 1904. 

 ^'Zeitseh. anorg. Chem., 12, 4. 1896. 



