30 THE ATOMIC WEIGHTS. 



Now, rejecting nothing, we may combine all the series into a general 

 mean, giving the weight of one litre of hydrogen as follows : 



First series 089938, .000007 



Second series 089970, .00001 1 



Preliminary series, second method 089921, .0000271 



Third series 089886, zfc .0000049 



Fourth " 089880, .0000187 



Fifth " 089866, .0000034 



General mean 089897, zfc .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, 



O = I5 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 this ratio. Its probable error, however, is given 

 too low ; for some of the oxygen weighings involved reductions for tem- 

 perature and pressure. These reductions involve, again, the coefficient 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. 



In a memoir of this kind it is impossible to do full justice to so elab- 

 orate an investigation as that of Morley. The details are so numerous, 

 the corrections so thorough, the methods for overcoming difficulties so 

 ingenious, that many pages would be needed in order to present any- 

 thing like a satisfactory abstract. Hardly more than the actual results 

 can be cited here; for all else the original memoir must be consulted. 



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 : 



*Zeitschr. Anorg. Chern., 12, 4. 1896. 



