COMPARISON OF DIFFERENT KINDS OF ALUM. 2l83 



not appear to US capable of being abridged, we shall give it 

 entire. 



Convinced, sav they, by tlie preceding oxperiments, that All the alums 

 the alums of which we iiave spoken are formed of the same J.'^^lf ^ronrSie 

 quantities of sulphuric acid, alumine, potash, and water ; sulphate of 

 and that they may be considered as identical, differing ^^^^^'^ 

 only by a thousandth part of sulphate of iron, we began with 

 examining, whether their action in dyes were as different as is 

 commonly asserted. Desirous that this part of our labours 

 should not be inferior in precision to the former, we endeavour- 

 ed to remove every cause of uncertainty that might occur ei- 

 ther fro^u the mixture of the colouring matters or the substance 

 dyed, the variations produced by the time or vessels employed 

 iji the application of the monlant, the unequal body of liquor, 

 or the ditTerence of temperature in the baths of dye. As we 

 w«re anxious to observe with the greatest care all the effects, 

 that might present themselves in the course of our experi- 

 ments, we performed the greater part of them ourselves, and 

 all the rest were executed under our inspection in our own 

 dyehouse. 



We have not laid before the Institute the results of more 

 than five hundred experiments with dyes that we have made, 

 the greater part of which served only to point out our course, 

 or confirm facts we had already observed : all those we have 

 suppressed would have added nothing to the various proofs we 

 set before them. 



All our researches were made at the Gobelins: we could- 

 not choose a dyehouse more convenient, or offering us more 

 advantages; for the processes there constantly carr;ying on, 

 to supply the demands of three imperial manufactories, ena- 

 bled us to make without interruption very numerous and 

 varied experiments, which could not have been executed 

 elsewhere without considerable expense. There we found 

 every thing we wanted, whether of vessels, dyes, or matters 

 to be dyed; and no where else could we have been assisted 

 by a more able dyer than our foreman, Mr. Blondeau, 

 who to great skill in colours adds very extensive practical 

 knowledge. 



Art. 



