for Chemical Purposes. 191 



consistence ; this is very expensive, on account of the high 

 price of pipe clay, which is about ten shillings the hundred 

 weight, whereas I employ in my improved mode of making 

 them the coarser kind of Stourbridge clay, u hich can be had 

 at the lilass-houses, in the ground state, for six sh llings the 

 hundred weifi;ht, and this I sift also, to stparaie the finer 

 part, which I employ for making other smaller articles ne- 

 cessary in my business ; using onlv ihe grosser or coarser 

 part for muffles, to which [ add one-eighth part only of pipe 

 clay, mixinsi them well together wiih water, so as to form 

 a mass of a pretty thick consistence. The tin mould bting 

 first greased, I place it in the frame Fig. 15, shown under 

 Fig. 1, and having spread ihe composition lu the mould, 

 and snioollied it with the spreader, Fig. 5, till the mould is 

 quite full, the flat piece of tin is then to be well greased, and 

 thrust in at one end of the mould, and the back of the 

 muffle is then formed by spreadinii the composition, and 

 firmly pressing it against the part a!read\' formed. The next 

 thing to he done is to cut the holes in the sides of the muf- 

 fle, which is done by pressing the semicircular cutter. Fig. 3, 

 into the sides thereof, while it is yet wet, and bringing the 

 pieoe out entire: the tin niould must now have the frame, 

 Fig. 4, put in to keep the sides ot tlie nuiffle from contract- 

 ing, and being set up end-wavs, and a little inclined, it 

 nuist be dried in the sun, until it has shrunk suffieiesuly to 

 leave the mould, after which it must be completely dried 

 and burned in the usr.al maniRT. 



The composition of the smaller implements, or muffle 

 bottoms for dial plates, for the mould Figs, y and :0, is 

 made of the finer part of the Stourbridge clay, with a small 

 proportion of pipe ciav. 



The rings are made from two pnrts of Dutch black lead 

 pots, piwdtied, and one part of pipe clay. I have made 

 repeated trials of English black lead, in various slates, as a 

 substitute for the Dutch black lead pots, but without find- 

 ing it to answer properly. 



Should any difficulty appear in any part of my process, 

 I shall be happy in attending the commitfees, and per- 

 fornsing the whole opcraliuii belyre them, whenever they 



shall 



