88 Messrs. V. H. Veley and J. J. Mauley. 



IV. Determination of the Concentration of the Samples. 



It is believed that in the majority of cases the mean error does not 

 greatly exceed one part per thousand. In every case the determinations 

 of the concentration of the samples were conducted either immediately 

 before or after those of the densities or refractive indices, as the most 

 concentrated acid is as hygroscopic a substance as sulphuric acid. 



In order to show the degree of concordance obtainable from various 

 methods the following cases may be cited. 



The value of a certain soda solution was determined at constant 

 temperature as against a certain hydrochloric-acid solution; using 

 variable quantities five values were obtained with a mean error of 1 

 part in 2844 parts, calculated by the method of least squares. The 

 hydrochloric acid solution had previously been standardised on two dif- 

 ferent occasions ; at one time as against recrystallised silver nitrate and 

 purified sodium carbonate, and at the other against another sample of 

 silver nitrate of presumably different past history ; the mean error by 

 the one method was 1 part in 1850 parts, and the total mean error 

 by the two methods was 1 part in 1298 parts. 



The same solution was determined twice as against a certain sul- 

 phuric acid solution, the value of which was ascertained by determining 

 its density at 15/4, ascertaining its percentage strength by interpola- 

 tion from Pickering's tables, and hence the amount of acid in 1 c.c. 



The results of all the determinations may be summarised as follows, 

 and expressed as nitric acid equivalent to soda in 1 c.c. 



(i.) By hydrochloric acid method = 0*06136 gramme 

 (ii.) By sulphuric = 0-06144 



Mean 0-06140 



Namely, a mean error of 1 part in 1533 parts. 



By soda it is desired to imply alkalinity only ; the metallic sodium 

 used for its preparation might have and probably did contain small 

 quantities of other alkaline metals, but as such soda solutions merely 

 served as go-betweens to express the one acid in terms of the other two 

 the possible effect of such impurities is thereby eliminated. 



Attention has recently been drawn to errors in burettes, not only by 

 the Eeichsanstalt of Berlin but also by individual writers, especially 

 Wagner ;* these errors may be summed up as those of (i) Parallax, 

 (ii) temperature, and (iii) drainage. The last of these varies, of 

 course, with the length drained, the viscosity of the solution, and the 

 often wholly unknown condition of the cleanliness of the glass. 



* 'Zeits. Physikal. Che:n.,' vol. 29 (1839), pp. 193-219. 



