i6o Microscopical Essays. 



While this is (landing, put into a bafon two ounces of quick 

 lime, and an ounce of orpiment ; pour upon them a pint and a 

 half of boiling water ; ftir the whole together, and when it has 

 flood a day and night, it will be fit for ufe. This is the liquor 

 probatorius vini of fome of the German chemifls' : it difcovers 

 lead when wines are adulterated with it, and will fhew it any 

 where. 



Put a little of this liquor in a tea-cup, and plunge the piece of 

 rind half-way into it. 



In the former part of this experiment, the veffels of the rind 

 have been filled with a folution of lead, that makes of itfelf no 

 vifible alteration in them ; but this colourlefs impregnation, when 

 the orpiment lixivium gets to it, becomes of a deep brown; the 

 veffels themfelves appear fomewhat the darker for it; but thefe 

 dots, which are real openings, now are feen to be plainly fuch, 

 the colour being perfectly vifible in them, and much darker than 

 in the veffels. This objecl mufl be always viewed dry. 



If a piece of the rind, thus impregnated, be gently rubbed 

 between the fingers, till the parts are feparated, we fhali be able 

 in one place or other to get a view of the veffels all round, and of 

 the films which form the blebs between them. 



Every part of the rind, and every coat of it, even the inter- 

 ftitial place between it's innermoft coat and bark, are filled with a 

 fine fluid. The very courfe and progrefs of the fluid may be 

 ftewn in this part, even by an eafy preparation : only that 

 different rinds mufl be fought for this purpofe, the veffels in fome 



being 



