VOL. XXXV.] PHILOSOPHICAL TRANSACTIONS. 30» 



for a certain time, and when taken out, scouring them with sand. By this me- 

 thod a woman may clean more plates in an hour than the most expeditious work- 

 man can file in many days. 



Of these waters the author mentions several; but what the Germans them- 

 selves used, and which they make a great secret of, he found to be only com- 

 mon water made eager with rye, which requires very little pains. For after 

 they have ground the grain roughly, and pounded it, they leave it to ferment 

 in common water for a certain time, and with a little patience they are sure to 

 have an eager menstruum. 



With this menstruum they fill troughs or tuns, into which they put piles of 

 plates; and to make it grow eager the better, and to have more activity, they 

 keep these vessels in vaults or stoves which have little air, and in which they 

 keep lighted charcoal. The workmen go into these vaults once or twice in a 

 day, either to turn the plates that they may be equally exposed to the action of 

 the acid liquor, or to take out those that are sufficiently cleansed, or to put 

 others in their room: and as the liquor is more acid, or the heat of the vault 

 or stove is more intense, the plates are sooner cleansed; but it requires at 

 least two days, and sometimes a great deal more. 



This is the method which the Germans employed in the tin-works in France, 

 constantly made use of, to prepare the iron-plates to receive the coat of tin: 

 but as the author observed, that the constant attendance on them in the stoves 

 was very laborious, the heat therein being almost insupportable to those who 

 are not used to it, he proposes some other methods, which are attended with 

 very little trouble, and as small, if not a less expence; and which on trial suc- 

 ceeded full as well. 



Having therefore observed that the iron-leaves or plates are covered with a 

 scale or layer, half vitrified by the fire, on which acids have none or very little 

 effect, he imagined, that instead of dissolving the iron in these acid waters, it 

 would be better to make it rust, and thereby put it in a condition to be easier 

 cleansed from these scales; as rust is accompanied with a sort of fermentation 

 and rarefaction, and the matter which rusts takes up a greater space, and raises 

 up whatever opposes it. To this purpose he steeped iron plates in different 

 eager menstruums, as in water in which alum, common salt and sal-ammoniac 

 were separately dissolved; and others of the same iron he only dipped into the 

 same waters, and instantly taking them out exposed them to the air. These 

 latter were rusted by all of them, but sooner by that in which the sal-ammo- 

 niac was dissolved. After two days, during which every plate had been dipped 

 into the menstruum but twice or thrice, he scoured them, and likewise those 

 he had left to steep for that time; and comparing them together, found that 



VOL. VII. R R 



