354 Tranjition of a /pedes of Flies, from 



that, after each procefs of vapouring, the fluffs be rinfed " al r 

 ways in water a little foapy, made with 2oz, of that fubftance 

 for each lb. of wool. " It may be neceffary to caution thofe 

 who have never made any experiments in bleaching with ful- 

 phureous acid vapour, that ioap even of the very beft quality 

 will always give the fluffs a. yellow tint, and that too though 

 it be ufed in only i-4th the quantity here prescribed. In- 

 deed, from a number of .experiments made about three years 

 ago, (which I now quote from memory) I am convinced, 

 that to attain a bright white, by the ufe of foap after the ful- 

 phureous acid, will be a very difficult, if not impracticable, 

 attempt. Ofiilk I may venture to (peak more pofitively ; 

 that the brighteft white pofhble to be made, cannot be pro- 

 duced where foap has been ufed after the fulphuring procefs. 

 It is in vain, however, to have recourfe to the expenfive and 

 dubious effort of foap, when weak alkaline leys are equally 

 fafe for the fluffs, much cheaper, and much more certain of 

 producing a bright white. In fome peculiar kinds of filk, 

 where the fulphureous acid vapour, (applied nearly in the 

 fame manner as directed in O'Reilly's valuable effay) the oxy- 

 muriatic acid, with foaps and alkaline leys, have all failed to 

 produce a bright white, it has been effected by a mixture of 

 iulphuric and muriatic acids, diluted fo as not to impair the 

 texture of the cloth. The proportions of the latter I cannot 

 at prefent fpecify. 



J.A.B. 



Tokenhoufc-Yard, Aug. 25,1801. 



LIX. FaSis ref peeling the Tranjition of a Species of Fly, 

 from the Chryfalid to the Volatile State. By Mr. John 

 Snart, Optician *. 



SIR, 



TTooley-Street, London. (No. 209,") Aug. iK. 

 HE following particulars, the refult of feveral hours ob- 

 fervation, which I made upon the development of a fpeciesof 

 fly from the chryfalis or pifcatory to its volatile ftate, may 

 prove acceptable to your readers ; and the more fo as it feldom 

 happens that people chance to be in thofe circumftances 

 which can make them witnefs the facts I mean briefly to 

 defcribe : 



June 7th, being Sunday, Fahrenheit's thermometer at 75°, 

 I obferved in a water-but, which had not been cleanfed for 

 jiear three weeks, a final I annulated and variegated worm 

 * Communicated by the Author. 



rifing 



