15.
Doe not expect to extract the eſſence of any vegetable unleſſe by making uſe of the feces, left after diſtillation: for if you take thoſe feces, as for example of a nettle, and make a decoction thereof, and ſtrain it and ſet it in the froſt, it will be congealed and in it will appear a thouſand leaves of nettles with their prickles, which when the decoction is again reſolved by heat, vaniſh away, which ſhewes that the eſſence of the vegetables lies in the ſalt thereof.
16.
In all your operations, diligently obſerve the proceſſes which you read, and vary not a little from them, for ſometimes a ſmall miſtake or neglect ſpoiles the whole operation, and fruſtrateſ your expectation.
17.
Try not at firſt experiments of great coſt or great difficulty, for it will be a great diſcouragement to thee, and thou wilt be very apt to miſtake.
18.
If any one would enter upon the practices of Chymiſtry, let him apply himſelf to ſome expert artiſt for to be inſtructed in the manuall operation of things, for by this means he will learn more in 2. moneths, then he can by his practiſe and ſtudy in 7. years, as alſo avoid much paines and coſt, and redeem much time which elſe of neceſſity he will looſe.
19.
Enter not upon any operation, unleſse it be conſiſtent with the poſſibility of nature, which therefore thou muſt endeavor as much as poſſibly may be, to underſtand well.
20.
Doe not interpret all things thou readeſt according to the literal ſenſe, for philoſophers when they wrote anything too excellent for the vulgar to know, expreſſed it enigmatically, that the ſonnes of Art only might underſtand it.
21.
In all thy operations propoſe a good end to thy ſelfe, as not to uſe any excellent experiment that thon ſhalt diſcover, to any ill end, but for the publick good.
