468 J. I. Phinney — Barium Sulphate in Analysis. 



with the irregularity of their amount."* The mean of all the 

 heights is 0*396 inch. The least annual mean is 0*072 and the 

 greatest 0*936; the difference between them, 864, is more 

 than double the mean of the whole series of observations, 

 which indicates the existence of a disturbing cause of the same 

 order of magnitude as the quantity to be measured, so that we 

 can draw no inference either way. 



I submit, therefore, that the title of this article has been 

 justified, and that it has been shown that rigidity cannot be re- 

 lied upon as affording a datum towards estimating the earth's 

 age. 



Art. LV. — On the Treatment of Barium Sulphate in 

 Analysis ; by J. I. Phinney. 



[Contributions from the Kent Chemical Laboratory of Yale College — XXIII.] 



In a recent paper by M. Ripperf entitled "Beitrage zur 

 Gewichtsanalyse der Schwefelsaure " the method discussed is 

 the precipitation of barium sulphate from an excess of the 

 chloride and differs from similar methods only in the manner 

 of purification of the precipitate. Purification according to 

 Ripper, is accomplished by oxidizing with bromine water what- 

 ever sulphate may have been reduced by the ignition of the filter, 

 then treating the entire precipitate with dilute hydrochloric 

 acid until the impurities are removed. In the course of his 

 investigation Ripper made the attempt to eliminate the pos- 

 sible source of error in the reduction of the sulphate by the 

 use of the asbestos filter-crucible, but finding it impossible to 

 bring asbestos to a sufficiently constant weight either by itself 

 or when treated with dilute acid, he abandoned it as impracti- 

 cable, and substituted the treatment of the reduced precipitate 

 with bromine. Ripper accepts without investigation the old 

 method of purifying barium sulphate by hydrochloric acid. 



Inasmuch as the asbestos crucible has been employed suc- 

 cessfully even in processes so delicate as atomic weight deter- 

 minations, sufficient confidence was felt in it to warrant testing 

 by its use the accuracy of the hydrochloric acid process of 

 purification, in this way reducing the necessary manipulation 

 and completely avoiding the introduction of bromine. Further- 



* Appendix to the writer's "Physics of the Earth's Crust," 2d ed., p. 34, 

 where a table of the annual heights and lags are given, compiled from the 

 u Results of the Harmonic Analysis of Tidal Observations," by Major Baird and 

 Prof. Darwin, Proc. Roy. Soc, vol. xxxix. p. 135, 1886. 



f Zeit. f. anorgan. Chem., ii, 36. 



