Part IV. Of Things relating to Chymijlry^&c. .355 
When five or fix Drachms are fiim'd away, take the Diih 
nimbly out of the fire, fo foon as the Salt laft put in is dry. 
If you have wrought well, what remains in the Difh will 
be yellowiih in fome parts, and every yellow part will (hine. 
Secure this Matter from the Air by fitting and cementing 1 
a Qlafs to it : otherwife it will loofe its property in one 
Week. 
As to the Caufe of this ftrange Vhomomenon^ Dr. Slave 
continues to this effect. I ihall in fhort offer my Thoughts, 
and refer them to your Judgment. Two Queftions may 
anfe : What it is in this Mixture that yields the light ? and, 
How it doth it ? As to the firit, I take it to be the pure fiery 
part of the Spirit of Nitre embraced by the Chalk, For 
that the reft is weak and phlegmatick 3 as appears, if it be 
diftiird. Alfo, that about the end of the Operation, a black 
Fume begins to rife and fly away. That if by continuing 
the Dilh too long in the fire, you drive all the Nitrous parts 
away, the Chall^ which flays behind will not be luminous. 
Or if the Matter duly prepar d, be cxpofcd to the Air, and 
thereby prey'd upon, the fame effect will follow. 
As to the Second, I fuppofe, That it Oiines not by Imbi- 
bition of Light, but by Imprcflion from it, from whence 
proceeds a motion therein productive of Light. Which 
we may the rather be induced to believe, In that if it be 
put into an Iron Cover, and then an Iron Box, and a good 
heat given to it, it will fhine fo vigoroufly as to feem to 
kindle the Air about it. That two Men by following their 
blow clofe, will make a Bar of Iron glow, or fhine in the 
dark. And although the Impulfe of Light may feem fmall 3 
yet upon Bodies nearly related to it, as This fcems to be, it 
appears to be great. As in thofe odd effects it fometimes 
hath upon Infants unus'd to it 3 and People that have fore 
Eyes 5 or have been newly Couch'd 3 as it happened to 
Dr. Caflle fometime fince, who by making bold with his 
Eyes too early, ( /. e. by a too frequent admirlion of light 
to them, ) after that Operation, did thereupon fuffer fuch 
extreme pains, and mifchief in his Eyes, that he now difpairs 
of ever feeing more. 
Mr. Haac (a) faith he, hath frequently repeated dre-W Author 
following Experiment upon this Phofyhorm. If it be ex- rinJJ^n 
pofcd to the Morning Light a little before Sun riling, it*^ L °^- 
Zz 2 prcfents« rt 3- 
