, 
Account of an electrical Increaser. 47 
thrie acid presents; many others remain to be noticed which my 
limited time did not permit. I have demonstrated that the red- 
dening of erythric acid depends on a loss of oxygen; that in the 
union of this acid with bases the same modified causes produce 
various colours, and that contemporaneously the erythric acid is 
transformed into another peculiar acid. Though these facts are 
not perhaps in all parts proved with the highest rigour, yet 1 
hope that they have such a degree of probability, that chemists 
will not refuse to admit their truth, until new researches shall 
demonstrate their fallacy. 
APPENDIX. 
In the first part of this memoir | have noticed some pheno- 
mena which occurred in the red washings of the spots made by a 
soluticn of uric in nitrous acid. Now that erythric acid is known, 
it is much easier to account for these. 1 had then observed that 
the washings exposed toa strong fire lost their colour. This, in- 
deed, ought to take place, heat having the power of dissipating 
or destroying the red colouring matter (5:9). I have then found 
that the alkalies and earths renew this colour. This may be easily 
explained, admitting that the very small quantity of erythric acid 
(7) which remains in those solutions is found disposed to be- 
come altered from the bases, and hence to produce new colour- 
ing matter (21). Finally, I have remarked that some metallic 
solutions precipitate the colouring matter, rendering it of a vio- 
let colour, and others make it yellow without producing a preci- 
pitate: for this | cannot adduce any plausible reason, and only 
consider that the solutions of those metals, which with ervthric 
acid produce insoluble salts, are those which precipitate the co- 
louring matter. Of the rest, I must frankly confess that the 
above-mentioned appearance and disappearance of colours are 
not always constant: this, however, in such compound and vo- 
luble substances is not very surprsing. 
VI. Account of an electrical Increaser for the unerring Mani- 
festation of small Portions of the Electric Fluid. Invented 
by Henry Urtneror, Esq. of Blair’s Hill, Cork. Com- 
municated ly Dr. PEARSON. 
Letter from Mr. Upington to Dr. Pearson. 
Blair’s Hill, Cork, Feb. 24, 1817. 
Sir, — Tue electrical increaser for the unerring manifestation 
of exceedingly weak and small portions of the electric fluid, re- 
specting which I took the liberty of addressing you on the 4th 
instant, was constructed by myself in the year 1510, for my pri- 
vate experiments; and at the same time I communicated its 
properties 
