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examination. The former is submitted to a powerful electro-magnet set in 
action by six to eight Bunsen elements. All the ferruginous parts are thus 
removed. The chemical treatment consists in the use of concentrated 
hydrofluoric acid for a short time. This process has been applied success- 
fully in an examination of the lavas of Santorino. 
IIoio to Prcpcii’e Triferrous Phosphate is a question answered in a paper at 
one of the late meetings of the Chemical Society, by Mr. R. Schenck, 
who prepared this substance by pouring a solution of ferrous sulphate into a 
flask in which phosphoretted hydrogen was being evolved by the action of 
potassic hydrate on phosphorus. The precipitate of ferrous hydrate at first 
formed rapidly becomes grey, and finally black. After removal of the 
phosphorus, the iron phosphide was purified by boiling it with a solution of 
potassic hydrate, and subsequently with hydrochloric acid. The results of 
the analyses corresponded to the formula FegP 2 ; the phosphorus appearing 
to be trivalent. The ferrous phosphide dissolves slowly in boiling acids, 
with evolution of gas, and in the dry state takes fire below 100°, burning to 
a reddish-brown powder. The author intends to apply the same method to 
the preparation of other phosphides. 
Silk Dyeing. Does Silk form Compounds with Acids ? — M. E. Durwell, who 
has a paper on this question in a late number of the Paris “ Bulletin de la 
Society Chimique,” takes for the foundation of his views the hypothesis 
that silk forms, with acids, true compounds, capable of uniting with the 
coal-tar colours and with other dyes. Having ungummed silk to set the 
fibroine at liberty, he boiled it for a day in distilled water, to remove the 
last traces of the soap employed in this operation. It was then extracted 
with alcohol, so as to leave pure fibroine, which invariably gave an alkaline 
reaction. This silk was then dyed in a bath of litmus and very dilute sul- 
phuric acid. The litmus serves here at once as reagent and as colouring 
matter. The colour is thus entirely fixed in the silk ; but, on neutralising 
the bath with a trace of magnesia or of caustic soda, the blue litmus went 
back into solution, except a trace which was still absorbed by the silk. 
This experiment may be indefinitely repeated on the same colour-bath by 
rendering it alternately acid or neutral. It is the same with the coal-tar 
colours; but as these have a great tinctorial power, the experiment is less 
striking and decisive than with litmus. On treating two parts of fibroine 
with one part of sulphuric acid in the cold, combination at once takes place. 
Heat is developed, which must be kept down as much as possible by cooling 
the capsule, otherwise the silk will be completely resolved into glucose and 
ulmic compounds. After an hour’s time, the reaction is complete. The 
brown liquid is filtered over asbestos, diluted with three or four times its 
bulk of water ; the excess of acid is neutralised with baryta, filtered, and 
evaporated. A mass is thus obtained which, on treatment with alcohol, 
leaves a true compound of fibroine and of sulphuric acid. It is a white, 
transparent, horn-like body, soluble in water. The solution, if treated with 
an alkali, gives a precipitate of fibroine. 
