254 On Bleaching, isfc. 



IV. 



Extraif of a Letter on the At of Bleaching, and the Eff'eSl of Friction in Water-courfes for 



Mills. By a Correffondent. 



A. 



^FTER giving a fliort ftatement of Mr. Higgins's procefs for making and applying 

 *he fulphuret of lime to the bleaching procefs, of which the entire account is given in the 

 following article, from the v/ork itfelf, fent by the fame friend ;* the writer proceeds as 

 follows : 



" The advanced price of alkaline aflies makes an economical ufe of them indifpenfable. 

 The above procefs renders them unneceffary altogether. How it may fucceed in the large 

 way is yet to be tried. There is another way to obtain the advantage of reducing the ex- 

 pence of bleaching with alkaline afhes ; that is, to apply to the Tquor, whenfaturated with the 

 colouring matter of the cloth, fome cheap (if any fuch there is) fubftance having a greater 

 affinity for the colouring matter than the alkali. The writer of the article Bleaching, in the 

 fupplement to the Encyclopoedia Brittanica, No. 5, fays, ' that if unto the alkaline folution 



♦ of the colouring matter of lime or lime water be poured, a copious precipitate falls down, 

 ' which confifts of the colouring matter and lime combined; lime, therefore, has a greater 



• affinity for the colouring matter than the alkali.' 



'" This is furely an error. I have not been able, by adding lime water to the alkaline folu- 

 tioa of the colouring matter, to obtain any confiderable precipitate. The brown colour of 

 the precipitate was not more changed than it would be by being fo much more diluted ; any 

 precipitate which there was, appeared rather to be occafioned by the carbonic acid difcom- 

 pofing the lime water. 



" The writer of the article, if he has fucceeded as he has ftated, has made a valuable 

 difcovery. 



" Kirwan, in his experiments on the alkaline fubftances ufed in bleaching, «c.* fays lime 

 diflblved very little of the colouring matter. 



" Mr. Nicholfon's thoughts on this fubjeft will gratify a friend to his Journal. 



" On Water Courfes for Mills. 



" Allow a water-wheel 8 feet in breadth ; it is required to know what width the canal muft 

 be to bring on the water to the wheel with full eSedt; fuppofing the length of canal to be 

 loo yards, and as the fri£tion of the water in the canal is in proportion to its length, what 

 allowance in width muft be given in any given length to compenfate for the oMlrudtion 

 arifing from that caufe ? The form moft advantageous is taken to be that defcribed by three 

 fides of a hexagon. 



" Londonderry. « A." 



• Iriih Tranfaftions for 1789. 



It 



