OBSERVATIONS ON FERRIC HYDRATE. 
652 
atomic number of fluorine lies between that of oxygen and chlorine ; and the atomic 
number of oxygen, added to that of fluorine, nearly equals that of chlorine. 
B. Aqueous Hydrofluoric Acid. 
Under the head of the aqueous acid the author enumerates the various impurities 
usually contained in the commercial acid, and describes the modes he employed to detect 
and estimate them, and to estimate the amount of HF in it. The process employed by 
him for obtaining the aqueous acid in a very high degree of purity from the commercial 
liquid is also fully described. It consists essentially in passing an excess of sulphuretted 
hydrogen through the acid, then neutralizing the sulphuric and hydrofluosilicic acids 
present by carbonate of potassium, decanting the liquid after subsidence of the precipi¬ 
tate, removing the excess of sulphuretted hydrogen by carbonate of silver, distilling the 
filtered liquid in a leaden retort with a condensing-tube of platinum, and, finally, 
rectifying. 
The effect of cold upon the aqueous acid was briefly examined, the result being that 
a comparatively small amount of hydrofluoric acid lowers the freezing-point of water 
very considerably. 
The chemico-electric series of metals, etc., in acid of 10 per cent, and in that of 30 
per cent, were determined. In the latter case it was as follows:—Zinc, magnesium, 
aluminium, thallium, indium, cadmium, tin, lead, silicon, iron, nickel, cobalt, antimony, 
bismuth, mercury, silver, copper, arsenic, osmium, ruthenium, gas-carbon, platinum, 
rhodium, palladium, tellurium, osmi-iridium, gold, iridium. Magnesium was remarkably 
unacted upon in the aqueous acid. The chemico-electric relation of the aqueous acid to 
other acids with platinum was also determined. 
Various experiments of electrolysis of the aqueous acid of various degrees of strength 
were made with anodes of platinum. Ozone was evolved, and, with the stronger acid 
only, the anode was corroded at the same time. Mixtures of the aqueous acid with 
nitric, hydrochloric, sulphuric, seienious, and phosphoric acids were also electrolysed with 
a platinum anode, and the results are described. 
OBSERVATIONS ON FERRIC HYDRATE, THE SO-CALLED SOLUBLE 
PEROXIDE OF IRON. 
BY PROFESSOR ATTFIELD, PH.D. 
In a memoir, noticed in the * Chemical News’ of June 12 as having been recently pre¬ 
sented to the Academy of Sciences, M. Jeannel, in allusion to the fact that ferric hy¬ 
drate is not always soluble in acids, states that the incomplete solubility is, in his 
opinion, generally due to the influence of traces of sulphates. He says, according to 
the Paris correspondent of the ‘ Chemical News,’ “ sesquioxide, precipitated from the 
persulphate, is always to a certain extent insoluble, or yields unstable salts; the same 
is the case with the sesquioxide precipitated from the perchloride, when this has been 
contaminated by sulphuric acid, or equally when the alkalies employed as precipitants 
have been so contaminated, or, finally, when the ferric hydrate, precipitated from pure 
solutions by pure alkalies, has been washed with common water.” This explanation 
does not accord with my experience of the properties of ferric hydrates and oxyhydrates. 
Firstly, in England the ferric citrates and tartrates used in medicine are successfully 
made in large quantities by dissolving ferric hydrate, prepared from ferric sulphate, in 
solutions of the respective acids and acid-salts. Secondly, I have frequently seen moist 
ferric hydrate perfectly dissolve in solutions of acids or acid-salts, even though the pre¬ 
cipitate has been washed with common water containing sulphate of calcium, a final 
washing with distilled water having, for various reasons, been neglected. Thirdly, I 
have often noticed that pure ferric hydrate, soluble when freshly precipitated, becomes 
imperfectly so if long kept, moist or dry. It is true that when alkali is added to solution 
of ferric sulphate, instead of the latter to the former, an insoluble oxysulphate is preci¬ 
pitated, and a similar compound may, possibly, be formed under other circumstances; 
but ferric hydrate, properly prepared and fairly washed, is readily soluble if only it be 
used in the moist and recently precipitated condition, with a solution of acid or acid-salt 
which is not too weak, and the mixture be not boiled or even strongly heated for any 
