174 0« the true Form of the 



fquare pyramids, efflorefced in the air, and had none of the 

 charaftcrs of the acetat of copper. 



5th, The acetous acid, diCtilled feveral times on the oxyd 

 of niangancfcj attacks copper and dilfolves it, but too weakly 

 »nd in too fmall quantity for me to recommend this method. 



6th, The acetite of lead poured upon a folution of the ful- 

 phat of copper inimediatelv produces a decompolition trom 

 which there refults fulphat of lead, which precipitates itfelf 

 in a little time ; and acetat of copper, which remains info- 

 lution. By decanting the latter, and evaporating it to a pel- 

 licle in a copper kettle, you will obtain beautiful cryftals of 

 Venus. If you wa(h well the fulphat of lead, and prepare 

 it to be employed in painting, as white lead, this laft procefs 

 may become very advantageous. 



Cryftallifed verdigrifc is in great requeft for painting and 

 varnifliing, to which it fupplies lively and durable colours* 

 Chemifts obtain from it by diftillation that acid, the fmell 

 of which is verj- jTcnetrating, called radical vinegar and alfo 

 acetic acid. 



X. An Attoiipf to dc t ermine the ince Form and neccffary'. 

 Angles oj JVeathcr that ought to be given to f'ancs of' a 

 Vertical JFindmill as they recede from the Centre, Itft 

 undetermined by Mr. Smeaton. By Kichard HalL 

 GowER, in the Sea Service of the Honourable Eaji Indld 

 Company *'. 



o 



N reading Air, Smeaton's Experiments to difcovcr the 

 proper Confiruftion of Windmill Vanes, read before the 

 Koyal Society the 31ft of May and the i4thof Jime 1759, 

 I was forry to find that millwrights had hitherto been 

 without any fixed principle wherewith to give the vanes of 

 vertical windmills their proper degree ofweather. 



If it were required to determine by calculation the number [I 



• CominanicatcJ bv th« Author, 





