178 On the Uj'c of Oak Bark in dyeing Black, 



cipitate, where it cannot but diminiih the intenfity of the 

 black. In a word, to bo convinced of thefe truths, it will 

 be lufficient to give a comparative view of the two procefles, 

 and of their refults. We fhall fuppofe, therefore, a kettle for 

 twenty-five dozen of hats, as is the cafe in feveral manufac- 

 tories. That quantity will require twenty-five pounds of gall 

 nuts and the like quantity of fulphat of iron, about 150 or 

 200 pounds of logwood, and twelve pounds of acetat of cop- 

 per (verdegris), and from 100 to 125 pails of water. The 

 gall nuts and logwood muft be boiled for about fix or eight 

 hours, which will reduce the decoftion to about a third. 

 The fire is then diminiflied, to throw in, portion by portion, 

 the fulphat of iron and the verdegris. In this manner the 

 bath is prepared, and you plunge into it the felt or hats, 

 which are to be drawn out and again immerfed different 

 times, as experience has fliown that atmofpheric air contri- 

 butes a great deal towards the efHcacy of the operation of the 

 dye. There is fome difference in the method of manipula- 

 tion ; but this depends on the practices followed in different 

 DianufaAorics : in regard to the dofes, they are nearly every 

 where the fame. 



" The method of Dimo Stephanopoli confifts merely in 

 fubflituting oak bark in the flead of gall nuts in the proportion 

 of a half, that is to fay, twelve pounds and a half inftead of 

 twenty-five. It requires no other preparation before it is 

 employed than to be cut, or coarfely broke. 



" Th^s bark furniflies a dye much ftiller, as well as more 

 beautiful and more durable; and the operation becomes much 

 eafier, for it is hot fubjeft to what is called burning. It is 

 free from an immenfe quantity of fcdiment, which is found 

 in the bath when gall nuts are employed, and which com- 

 municates a duft that can be removed orily by a rod or 

 brufh, which, however, requires tedious and troublefomc 

 labour. ' 



" By forming an eftimate at the ufual prices, in the opera- 

 tion above nier.lioned, the gall nuts employed coft ']^ francs, 

 and the oak bark i4fous*. Janin^ in the ftreet Avoie, pro- 

 prietor of one of the largeft hat nianufa£lories at Paris, and 



* One hundredth of the price of the galls. 



who 



