On Standards of Weight and Mtafures. ,163 



with the iron, as is the cafe in various folders, the mere iron filings of the compound caa 

 not be fcparated in this manner. And fo likewife brafs, copper, and zinc filings, which 

 adhere to thofe of the iron, are likewife forced to obey the magnet, and render the opera- 

 tion fo far ineffeftual. 



Sulphate of Iron, VHriolated Iron.— "Ph. L. 



Should confift; entirely of iron united to fulphuric acid. The vitriolated iron of the fliops 

 frequently contains copper, on account of its being in general prepared, by merely re-dif- 

 folving the common green vitriol of commerce, which abounds with copper. The befli 

 way of detefting the prefence of copper, conlifts in diflblving one part of the fulphate o£ 

 Iron, in three of diftilled water, precipitating this folutlon with carbonate of pot-afli, and 

 then letting fall into it a little ammoniac. If the fmalleft quantity of copper is prefent, 

 ihe fluid will acquire a fapphire blue colour, but no fuch effect will take place if the fait 

 be free from copper. 



The praftice of obtaining this fait pure, by diflolving the common green vitriol, and 

 fubfequent boiling with iron filings, or cryftalization in an iron veflel, is not fo fatisfaflory 

 .IS could be wifhed. Sulphate of zinc, which is frequently found in the common fulphate 

 of iron of commerce, does not become feparated in this manner. A dire£t combinatioa 

 isrcquifite for obtaining this fait perfectly pure. 



FRED. ACCUM. 



No. 3, Campion Street, Soho. , 



IV. 



ExtraBs of Letters from H. GooDWYNy Esii- on the Unities of Weight and Meafure heft 

 adapted to the Britifh Empire ; on the new Meafures of France ; with a Defcription of an 

 Engine for raifng Water. 



I 



APPREHEND it to be an indifputable point that a correfponding unity of weight and 

 meafure is truly defirable in this kingdom ; and that an additional benefit, beyond what the 

 French nation poflefs from their new metrical fyftem, would arife, if that unity corre- 

 fpondedalfo with the general method in which the comparative fpecific gravities of bodies arc 

 expreffed with us, namely, by an unit, or by one thoufandth part. Now, Sir, it appears 

 to me that we are not only in pofieflion, but in the conftant ufe of one, both for weijght 

 and meafure, as invariable as that now eftabliflied in France. I allude to the foot meafure 

 and avoirdupoife, or (if I may be allowed the more appropriate expreffion) decade ounce 

 weight. "When I add, what I am perfuaded, by your valuable publications, you well 

 know, that the decade ounce weight, of pure rain, or diftilled, water at 60° of heat, is 

 generally allowed to be equal in bulk to the -i^V^th part of the cubic foot ; and alfo ob- 



Y 2 fervc 



