354 ^"^•f- — R^M^^ of Sulphuric Ether. 



vance It to the maximum ; and this is the reafon why the acetates of iron pafs fo rapidly to a 

 red colour, that it is impofTible to obtain them green in a folid ftate. 



M. Proud prefers, both for durability and beauty, ink which is made by a folution of 

 iron in an infufion of the gall-nut, to that which is prepared from fulphate of fteel. 

 His reafons are plaufible. The infufion of acorns, concentrated and digefted with iron 

 filings, prefented the fame phenomena as the infufion of the gall-nut, and afforded M. Prouft 

 an ink, which, when mixed with a fmall quantity of vinegar and a fufficient quantity of 

 gum, was inferior to none in its good qualities. 



From the experiments of M. Prouft, it follows, that tliere is nothing except the red 

 oxide of iron which can make ink with the principles of the gall-nut ; that the fulphates of 

 iron, which are made ufe of for that purpofe by ink-makers, containing always different 

 quantities of red oxide, there as many different kinds of ink as there are recipes for 

 making of it; but let thefe inks be only once fpread upon paper, and the air reduces them 

 all to nearly the fame ftate. 



Every one is acquainted with the property poffelfed by inks which are too much diluted ; 

 of becoming black after they are fpread upon paper by the pen ; but this phenomenon may 

 be produced in a much more ftriking manner. It is only neceffary to pafs fome ful- 

 phuratcd hydrogen gas into the ink, and the black colour will inftantly difappear ; but 

 afterwards, in writing, it is very pleafant to obferve this, clear liquid become very fpeedily 

 black. 



Such are the principal fafls which have been communicated by M. Prouft refpeding the 

 combination of iron with the principles of the gall-nut ; namely, the tanning principle and 

 the gallic acid. They ferve to illuftrate the theory and the praftice of the arts of dyeing 

 and of ink making. He has promifed the Inftitute to purfue his refearches on this fubjedl 

 ftill further. 



In another article, M. Prouft propofes a method of obtaining fulphuric acid from the refidues 

 of the dijlillation of fulphuric ether. This fimple procefs confifts in diluting the refidue with 

 two parts of water, filtering through a cloth to feparate the coaly fubftance from it, and 

 fubjefting the liquid to diftillation in a glafs retort. When the acid has acquired 1.84 

 of fpecific gravity, from 4 to 6 grammes (parts) of faltpetre to each demikilogram (five 

 hundred parts) are added ; and the diftillation is continued till the fluid is perfectly white, 

 and weighs from 1.86 to 1.87, water being 1.00. 



M. Prouft prefers an iron frame to a fand bath to place the retort in for thefe diftil- 

 latlons ; and he gives very good reafons for the preference. He computes that the profit 

 of purifying the refidues of ether in this manner will be confiderable ; fince it affords 

 between a fourth and a third part of fulphuric acid concentrated to 1.87 fpecific 

 gravity. 



The fulphuric acid, feparated from the butuminous matter before it is redified, has been 

 fubjeded to fome experiments by M. Prouft. He obferved, that alkalis, as well as the 

 prufhatee, did not precipitate any thing. It abundantly decompofes hydro-fulphurated 



water 



