arid the InconvenUnu gJ .AJb CufeUs. 217 



the-conftruAion of ciipeils, as is the cafe in regard to the 

 !"ole.< of the reverberating furnaces in the ci-devant Brittany; 

 but it would be necelFary to ram this earth repeatedly for fe- 

 vera! days; otherwife it would fplit, and thcfe cracks would 

 increafe bv the fhrinking which muft rcdilt from the heat, 

 and Jead would infinuate itfclf into thefe tiflures : an incon- 

 venience which cannot take place with fand even a little 

 earthy. I fliall obferve alfo', that a fole of earth would har- 

 den too much to allow a gutter to be dug for the paflage of 

 the litharge : in this cafe it would be neceflary that the place 

 deftined for the oxide to run off fliould be conftrufted with 

 fand or lixiviated adies. 



I (hall. add alfo, that it will be advantageous to employ two 

 kinds of fand in the formation of the bafon of the cupell ; 

 one kind fine like that ufed bv founders, and the other coarfer 

 and not earthv : the latter will form th^ firft llratum, which, 

 after being beat with rammers deftined for that purpofe, ought 

 to be about three inches and a half in thicknefs. The fine 

 Hmd, a little earthy, muft then be applied over this firft ftratum 

 to form a fecond, which is to be rammed like the former. Both 

 thefe kinds of fand muft be fomewhat moiftened before they 

 are introduced into the furnace, in order that they may be 

 better henped up, and be confolidated by the rammers. 

 - TJie fand of t!ie lower ftratum, being coarfer than that of 

 tlic upper, will abfurb the moifture of the latter in proportion 

 as it evaporates ; and it will pafs without any obftacle through 

 the canals cifpolcd for th:it purpofe. 



The lower ftratum of fand may remain in its place when 

 a new cupell is to be conftruded with fine fand, and the part 

 of the latter, which has not been impregnated with oxide, 

 muft be mixed with new fnnd to form a cupell. Care muft 

 be taken in raifing this fand not to touch the lower ftratum; 

 for the fand of the latter, which is coarfe, muft not be mixed 

 with the other. This inconvenience may be avoided by 

 beating over the bed of coarfe fand a thin ftratum of afties, 

 ^t wliieh you muft ftop in removing the fine fand of the upper 

 ilratum. 



It has been faid that the founders' fand muft be fome- 

 what earthy, and ihnt, if it is not, a little argil muft be added 

 to give it C'lhcfion : but, as it is neceffary that this argil 

 ihould be unifonnly dlftufed through all the parts of the fand, 

 it muft be diluted in the water with which the fand is moift- 

 rtned, and the whole muft be carefully mixed. 



Jt may be nbjecHed, that as cupells of fand do not abforb 

 fo much litharge as thofc of aftics, more lime will be required 

 to terminate the operation of refining; fince^ in the new pro- 



ccfs. 



