210 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
Solutions of known strength were prepared of neutral sulphate of quinine and of 
hydrochloric acid. The quinine salt was employed warm, and it exhibited only a 
trace of fluorescence. The solutions were mixed in definite proportions, and the 
amount of visible fluorescence was noted. 
Sulphate of Hydrochloric 
quinine. acid. 
Character of fluorescence. 
1 equiv.+ 0*5 equiv. 
A deep blue entering far into the liquid. 
1 equiv. + 1 equiv. 
A more intense blue, and confined to the edges. 
1 equiv.q- 1'5 equiv. 
Much as the preceding. 
1 equiv. + 2 equivs. 
Rather fainter blue. 
1 equiv. + 3 equivs. 
Decreasing. 
1 equiv. + 4 equivs. 
Still decreasing. 
1 equiv. + 6 equivs. 
Fainter, 
1 equiv. + 8 equivs. 
Still fainter. 
1 equiv.+ 12 equivs. 
Very faint. 
1 equiv. + 20 equivs. 
Just visible. 
1 equiv. + 30 equivs. 
As above. 
1 equiv. + 50 equivs. 
Invisible except under the most favourable circumstances. 
It will be seen at once, that the double decomposition between the sulphate of qui- 
nine and the hydrochloric acid was not perfect. Had it been so, the first line of the 
experiment would have been represented by the formula — 
2(C«H,3N,0„ ho, S03) + HC1=C,,H,3N,0„ HCl-fC,,H^N,04, 2(HO, SO3), 
and the largest possible amount of fluorescence would have been obtained : while the 
second line would have been according to the formula — 
C,JI,3N,0„ ho, S03-fHCl=C,,H,3N,0„HCl+H0, SO3, 
and there would have been no fluorescence visible with this or any higher proportion 
of hydrochloric acid. But instead of single equivalents of sulphate of quinine and 
hydrochloric acid giving a non-fluorescent mixture, the blueness was only then attain- 
ing its maximum. After the addition of T 5 equivalent, more hydrochloric acid caused 
a gradual diminution of the amount of bisulphate of quinine ; and although the 
presence of undecomposed bisulphate was only observed as far as fifty equivalents of 
acid added, yet it was doubtless only the imperfection of vision that prevented the 
experiment being carried further. 
If this be the true method of interpreting the observed phenomena, and I imagine 
there can be no reasonable doubt that it is so, it shows that instead of hydrochloric 
acid having such an overwhelming tendency to combine with quinine, it is scarcely 
so strong in its affinity for that base as sulphuric acid is. Chloride of sodium was 
found to have even less pov.^er of decreasing the blue colour than an equivalent 
amount of the acid has. 
There is a slight source of error in the experiment just detailed, arising from the 
constant dilution of the liquid by the addition of the hydrochloric acid solution. 
This dilution, however, was very trifling, since strong acid was employed with a view 
to obviate it as far as possible. It will be evident that it cannot affect the general 
