Microscopical Essays. 



glaf's rod has contracted any fpots, it muft either be thrown away, 

 or the parts that are fpotted muft be cut off. 



The piece of tripoli which is to be ufed in forming the glo- 

 bules, mould be flat on one fide, and fo large, that it may be 

 handled conveniently, and protect the fingers from the flame. A 

 piece four or five inches long, and three or four inches thick, will 

 anfwer very well. The belt tripoli for this purpofe, is of a white 

 colour, with a fine grain, heavy and compact, and which, after 

 it has been calcined, is of a red colour. This kind refills the fro 

 beft, is not apt to break when calcined, and the melted glafs does 

 not adhere to it. To calcine this tripoli, cover it well all round 

 with charcoal nearly red hot, leaving it thus till the charcoal is 

 quite cold ; it may then be taken out. Let feveral hemifpherical 

 cavities be made on the flat fide of the tripoli ; they ffiould be 

 of different fizes, nicely polifhed, and neatly rounded at the 

 edges, in order to facilitate the entrance of the flame. The large 

 globules are to be placed in the large cavities, and the minuter 

 ones in the fmall cavities. The holes in the tripoli muft never be 

 touched with the finger. If it is necefTary to clean them, it fhould 

 be done with white paper ; the larger globules may be cleaned 

 with wafh leather. The glafs rods {hould be of various fizes, as 

 of i-ioth, i -20th, i~3oth of an inch in diameter, as clean and 

 free from fpecks and bubbles as poffible. 



To MAKE SMALL GLASS MlC R OSCOPIC GLOBULES. 



Take two rods of glafs, one in each hand, place their ex- 

 tremities clofe to each other, and in the pureft part of the flame; 

 when you perceive the ends to be fufed, feparate them from each 



B 2 other ; 



