162 NEW STEAM DIGESTER. 



As long ago as the year 1793 I applied my thoughts to r«i* 

 der this inftrument lefs imperfed, and though I cannot flatter 

 niyfelf with having fucceeded in any confiderable degree, a 

 (hort account of my attempts may not perhaps be thought quite 

 ufelefs. 

 The ufoal My firft obje6l was to obtain a perfect clofure for the digefter, 



clofwig the di- "'^'^'ch is necelTary not only for increafing the heat, but alfo for 

 gefter is faulty preferring the contents. In former contrivances this has ge- 

 in many ix- nerally been effefled by a metallic cover prefled on the top of 

 the veflel by means of fcrews, wedges or other mechanical con- 

 trivances, with a circular piece of leather, paper, or other foft 

 material between both. I alfo tried thefe methods in a great 

 variety of ways, but always found fuch covers either leaky, on 

 applying moderate prelTures, or when the preflure was ftronger, 

 too curaberfome for a courfe of varied and repeated experi- 

 ments. Befides which, at the degree of 260 or 270® Fahr. 

 the leather, as obferved before by Mr, Betancourt, is commonly 

 decompofed or burnt, and linen or paper ceafe to clofe at a ftill 

 lower temperature ; as foon as the moithire, they are imbibed 

 New cover wilh becomes converted into vapour. I therefore ufed another 



jvhjch fits by a ^^y,^^ Qp a particular kind, confining of a thick circular plate, 

 conical interior , ^ ' =» ^i • l 



furfacc, without With its edge turned conical, and grouud to fit exactly m the 



packing. under fide of a metallic ring of the fame conical form, folded 



to the mouth of the digefter, in which the plate was previoufly 

 included. When the vefTel was ready for experiment and the 

 plate lifted up fo as to apply to the ring, it clofed as exadly as 

 could be defired, and the increafed force of the fteam, which 

 tends to render other covers defective, had in this a contrary 

 effedt. Two difficulties were thus overcome, that of a cura- 

 berfome preffing apparatus, and the infufficiency of packings; 

 but as the circular plate in this conftru6^:on w^as made to re- 

 Inconvenlence main conftantly in the digefter, I found that though it was laid 

 of this coutri- j^^^^ i]^q U jg of \i^ \^ fome experiments this mode was atteixled 

 with an inconvenience which I was defirous of removing. I 

 fucceeded by making another circular ring, turned with both 

 fides conical, to be put between (he circular plate and the open- 

 ing of the digefter, fitting exactly to each of them. This ring 

 ab, Fig. 5. Plate iX. paftes over. the cover cd, when both are 

 lowered, the, ring remaining in thedigeftor; but the circular 

 plate is taken out through the enlarged opening ef. Though 



Iha4 



vaoce« 



