APPENDIX. 



" In every other refpeil M. Poifibnaier employs 

 " a ftill-head, worm-pipe, and worm-tub, with all its 

 " ufual apparatus; and he direds fix ounces of foffil 

 " alcali to be mixed with the fea water at each diililla- 

 " tion, to prevent the acid of the Magnefia fait from 

 " rifing with the vapour, when fait begins to form on the 

 " bottom of the ftill. It is probable that in M. 

 " PoilTonnier's Hill, which was even more fhallow in its 

 *' form than Mr. Hoffman's, fome of the water might be 

 " thrown up toward the worm ; in which cafe the pierced 

 *' plate with pipes might be of fome fervice in breaking the 

 *' direftion of the water. But by Do6tor Irving's tube 

 " this inconvenience is entirely prevented, as experience 

 " fully evinceSj viz. in a voyage to Falkland's Iflands, 

 " where it has been ufed in dlflillation every day; in 

 " feveral voyages to the Eaft Indies ; and in this voyage, as 

 " is mentioned in the Journal. 



" M. . Poiflbnnier, in correcting this error in the 

 " conftruftion of his llill, has introduced another of the 

 *' mofl: capital nature in diflillation. For by means of 

 " the pipe-cullender, the vapour will meet with the 

 " greateft refiftance to its afcent, which will retard the 

 *' progrefs of diflillation in a very high degree, and 

 " increafe the Efnpyreuf?ia. 



*' From all the experiments abovementioned, it 



*' is evident, that no method had hitherto been 



" invented of making fea-water frefli, which was 



I i " not 



209 



