340 . jBIack D^e.-^DouhU EleBhf Aiiraliiotis. 



acid, Immediately formed black. Hence he concluded that the gallic acid, or the aftringent 

 principle and the green fulphate, exifled together in the bath. The red fulphate which was 

 poured in, combined with the vegetable principle ; the oxygenated muriatic acid, by con- 

 verting the green fulphate into red, gave it the facility of combining and affording black 

 with the fame principle. 



From thefe fafts it follows, that, in the procefs of dyeing black, a portion of the blackening 

 principle, whether it be the tanning matter or the acid of galls, is deftroyed by oxydation ; 

 that a certain period arrives at which the bath canno longer afford the black dye, unlefs, by 

 expofure to the air, the iron can refume the quantity of oxygen neceflary to bring It to the 

 ftate of red oxyde ; and lafliy, that dyers would confiderably accelerate their work by ufing 

 the red fulphate. It would only be neceflary in. that cafe to provide againft the excefs of 

 fulphuric acid, which always is found in the fulphate of iron when it paffes from green to 

 red. "With regard to the ufe of logwood, verdigris, &c. Mr. Prouft is convinced th^ 

 thefe fubftances are not necefTary, and that the mod beautiful blacks may be obtained by 

 afiringents alone with iron. 



III. 



Notice of a Memoir of Citizen GuTTON, upon the Tables of the Compofttion of Salts, and the 

 Means of verifying the Proportions indicated by thofe Tables*. ' - 



A H E little agreement between the tables of Bergman, Wenzel, and Klrwan fliews all 

 the difHculty of determining with exadlncfs the proportions of the component parts of 

 falts. A method of verifying fuch tables would therefore be ufeful to the progrefs of fclence. 

 .The following appears fo fimple and appropriate, that it is aftonifliing it has not yet been 

 attempted. It confifts in a comparifon of the rcfults of experiment and computation, with 

 regard to the agreement of the very perceptible effect arifing from the excefs or deficiency 

 of one of the fubftances after mutual decompofition. 

 For example, according to Bergman : 



Sulphate of Barytes contains Acid 13.' 



Barytes 84. 

 Sulphate of Soda contains Acid 28. 



Soda 1(5. 

 Muriate of Barytes contains Acid 23,57 



Barytes 76,43 

 Muriate of Soda contains Acid 52. 



Soda 42. 

 Negleding the water, which, though of fome confequence in the efTefl, Is of none.In the 

 rcfult J we fee that, in the cafe of an exchange of bafes between two falts, the refult of the 

 mixture mufl either be neutral, or poflefs an excefs of acid, or an excefs of the bafe ; and 

 that, by rendering the decompofition of one of the falts complete, we ought to obtain the 

 fame refult from calculation as that which lliall be afforded by experiment. 



* Head to the National Inftitute of France, the 16th Praid»l, in the year V. This notice is tranflatcd from 

 the Annaks de Clumie, xxr. 292. 



Now, 



