92 CORRESPONDENCE OF RAY. 



menstruum, of which you inquired. The experiment was 

 made accidentally ; for having kept it in a glass phial 

 (part of the relics of which he showed me), and going to 

 take out some for their use, they found that it was all 

 run out, and yet they could observe neither crack nor hole 

 in the glass ; yet observing that the glass was very white 

 as far as it had been filled, he not imagining what might 

 be the reason, endeavoured to cleanse it with an iron 

 prepared for that purpose ; but the glass proved so ten- 

 der, that at the first touch the iron made a hole through 

 it. Upon this they began to consider what might be the 

 reason of this accident, for they had often made the same 

 preparation, and yet not met with this effect. At length 

 they remembered that they had by chance used a stronger 

 fire than they did formerly; and therefore, upon the next 

 occasion, after they had drawn part of it with their usual 

 degree of heat, towards the latter end they urged it with a 

 stronger fire, and found, according to their expectation, that 

 what was drawn first did not dissolve glass, but the latter 

 did. This experiment they have made four times with suc- 

 cess, and without failing at any time. They showed me 

 about a pint of their last extraction in a thick green glass 

 bottle, and it seemeth to have dissolved it about half-way 

 through. He seems to make a doubt of the meaning of 

 those words in your query (whether the menstruum dissolve 

 glass constantly and certainly) ; if you mean as I imagine 

 you do, you have your answer already. 



But if you ask whether the same portion of the men- 

 struum, which hath formerly dissolved glass, will again 

 do the same with the same vigour? He answers, that 

 in this particular it doth not differ from other ordinary 

 menstruums ; for at the second time it works its effect 

 more weakly, and the third time scarce discernibly, as he 

 hath observed. If, after this account, Mr. Boyle think 

 this a matter worth his consideration, he may absolutely 

 command Mr. Fisher in this particular, or any other, 

 without any conditions or reservations, as he may do all 

 that part of the world which pretends to ingenuity and 



