256 1'- HAÜA, AND Y. OSAKA. 



materials aJl prepared by each for his own use. The first and last of 

 the tables appended contain the results obtained bv Ha^a, and the 

 second those obtained by Osaka. 



For titration in the experiments recorded in Tal3le I and II, 

 decinormai solutions, in the experiments given in Table III twice 

 decinormai solutions oi' potassiiun and sodium hydroxides and of 

 ammonia were taken. I'hey were almost pure, containing only the 

 merest traces of si lien and alumina, but as these and also carbon 

 dioxide when present in noticeable quantity affect the indications of 

 some of the colour reagents, we were careful to determine for each 

 indicator the exact titre of the alkali solution in terms of a decinor- 

 mai sulphuric acid which hud been standardised gravi metrically by 

 barium chloride, thus rendering ourselves independent of the effects 

 of any impurities present. 



The hydrofluoric acid examined was purified in the following 

 way :— Commercial ■" piu-e " hydrofluoric acid solution was distilled 

 in a platinum retort after adding a lew drops of a saturated solution 

 of potassium permanganate and a little potassium hydroxide. The 

 distillation went on at about loO°C. The product was found to be 

 free from hydr<jchloric acid and other foreign matters. Silica was 

 sought for by Jorgensen's chloropurpureocobaltic chloride test, and 

 not found. Before piu-itication the acid gave a small qufintity of 

 precipitate on standing with this reagent tor three days, but the 

 distilled acid «^ave none after standinü" for a week. 



The purified acid was diluted and preserved for use in a gutta- 

 percha bottle which had for years been holding the acid before its 

 final puritication. For each titration, a portion was weighed off' in a 

 platinum crucible with well-fitting lid, and was then washed into a 

 large platinum dish in which the neutralisation was effected, except 

 that in some (.-ises the results recorded in Table I w^ere obtained bv 



