VOL. XIX.] PHILOSOPHICAL TRANSACTIONS. ]67 



tlie inward circle of the ring with it, so as to give it a mercurial tincture, and 

 being wiped dry, be fit for use. Then let it be laid on the table, and pour a 

 drop of quicksilver within it, which press gently with the ball of the finger, 

 and it will adhere to the ring; then cleanse it with a hare's foot, and you will 

 have a convex speculum. Take up the ring and speculum, carrying it hori- 

 zontal, and lay it on the brims of the hollow cylinder b ; so will the mercury 

 become a concave reflecting speculum, which, from the smallness of the sphere 

 of whicii it seems to be a section, may be used as a microscope. The cylindric 

 vessel B has a screw hole at bottom, by which it is screwed to the top of the 

 pedestal c d ; c e f g is the supporter of the object plate, which may be raised 

 higher or let lower, as there is occasion, by the screw on the pedestal ; the 

 object plate must be of glass, cemented to the ring g. 



This instrument, with a little variation, may be made a reflecting microscope 

 of water, if, instead of the ring g, there be only a small arm with a hole in it, 

 to receive a drop of water, and the cylindric vessel b be either taken away, or 

 screwed on with its bottom upwards, so as to make an object plate. And this 

 will be found more convenient for viewing the textures of opaque objects, than 

 that described in N° 223 of the Transactions, which is fitter for fluid and trans- 

 parent ones. 



Of a Red Colour produced by a Mixture of a Sulphureous Spirit with a Folatile 

 Alcali. By Mr. Edw. Coles. N° 228, p. 342. 



In making several chemical experiments, I found a sulphureous spirit, which 

 being mixed with a volatile alcali, such as spirit of sal ammoniac, or urine, &c. 

 gives it a red colour in a moment, and that without any eff'ervescence, though 

 both the liquors be clear before. And as this experiment may be serviceable in 

 demonstrating sanguification, it is humbly offered to your consideration, &c. 



I made the spirit by distilling 2 or 3 pounds of benzoin, with a little sand in 

 a retort, ad siccitatem, and putting the oil, spirit, and flowers altogether into 

 a paper filtre : the spirit comes first through. You may put two parts of the 

 spirit to one of spirit of sal ammoniac, or urine, &c. then shake the glass or 

 bottle, and it will be red in a moment : though the more the glass is shaken, 

 the deeper or blacker red it will be. 



A Note, communicated by Mr. Hill, confirming the great Age of Henry Jenkins.* 



N° 228, p. 543. 



In the king's remembrancer's office, in the exchequer, is a record of a depo- 



* See N° 221, p. 92, of this vol. 



