Langenhan—Tine Arsenical Solutions. 
143 
powder, 10 or tablet. The slow solubility of arsenic trioxide in wa¬ 
ter may be accelerated either by hydrochoric acid or by potassium 
carbonate. The question may well arise, are these adjuncts mere 
pharmaceutical conveniences or do the resulting reaction mixtures 
differ sufficiently chemically to make the products different thera¬ 
peutic agents'? If essentially alike as therapeutic agents, another 
pharmaceutical question may be asked, viz., are the two solutions 
required in medical practice to avoid chemical incompatibilities 
when prescribed with other substances? The first question is an¬ 
swered in the negative by modern pharmacologists. * 11 The socalled 
neutral solution being unstable, 12 the acid and alkaline solutions 
afford pharmaceutical advantages only. Both are official so that 
incompatibilities may be avoided by using either the one or the 
other. 13 
In a general way, the chemistry of these two solutions has cer¬ 
tain aspects in common, hence may be considered together if for 
no other reasons than to avoid unnecessary repetition. The reac¬ 
tions involved may be reviewed from the following points of view: 
A. ) The hydration of arsenic trioxide. 
B. ) The action of an alkali, such as potassium hydroxide or 
potassium carbonate, on the hydration products. 
C. ) The action of hydrogen chloride on the hydration products. 
A. Hydration of arsenic trioxide. 
When arsenic trioxide, arsenous acid anhydride, is dissolved in 
water, its hydration to metarsenous and other arsenous acids may 
be assumed. This hydration finds a ready expression in the fol¬ 
lowing structural formulas of these compounds : 14 
As^° 
\ II 
O + OH 
AS \\ 
O 
— -— 
Arsenous acid 
anhydride. 
10 In the French Codex of 1866 there was official a Poudre d’ Acide Arsenieux. 
11 See letters by Bernard Fantus, A. S. Loevenhart, and Torald Sollmann. 
“See letter by Dr. Withering, in Fowler’s Report, p. 124. 
m See letters by Dr. Fantus and Dr. Sollmann. 
14 'Similar formulas are used by A. Stavenhagen in his article on “Beitraege 
zur Kentniss der Arsenite”. Joum. pr. Chem. (1895) 159, p, 1. 
As—OH 
As—OH 
Metarsenous acid. 
