176 Memoir upon the Mordants 



standing this time, the silk was taken oilt of the liquid, 

 drained completely over the bath, and washed several times 

 with distilled water, to separate that part of the mordant 

 which had not combined with it. The alum bath and the 

 wai^hincs were then evaported with the greatest care, and 

 they afforded very transparent crystals of alum. These 

 first products indicated pretty clearly the nature of the 

 combination which had been formed with the silk during 

 the stcepine, and that the alum had not been decomposed. 

 The alumed silk was then boiled in a itiattras with six 

 quarts of distilled water, the boiling liquor was poured of? 

 from it, and in this manner it was treated twelve times. 

 The 72 quarts proceeding from these operations being 

 evaporated, we obtained well formed crystals of alum, the 

 quantity of which, added to that obtained from the bath, 

 amounted to within two decigrammes of the 95 grammes 

 oviiiinally employed, forming a loss of ^i-g- part only. If 

 after each of the twelve washings we attempt to dye the 

 silk, the colour is less deep, in proportion to the number 

 of washings, so that after the twelfth the silk is not at all 

 coloured. If the silk, after having thus been washed, is 

 aiiain impregnated with alum, it re-acquircs the same pro- 

 perty of retaining the colour which it had before the washing 

 commenced, tdence results a very natural explanation of 

 the reason why alumed silks take a deeper colour when the 

 dyeing is commenced at a low temperature, than when 

 they are plunged into boiling baths; it is because, in the 

 one case, the action of the boiling water upon the mordant 

 is so speedv, that there is not time for the colouring matter 

 to fix upon'it, and render the combination insoluble, whilst, 

 in the other case, no such effect takes place. 



Art, 2. — Analysis of the Impregnation of JVool with Alum, 

 After havifio; thus ascertained the ' phaenoinena which 

 take place in the aluming silk, it was necessary to continue 

 the trials upon wool, and to employ for these experiments 

 only perfectly pure materials, completely deprived of the 

 carbonate of lime, which is generally contained in consi- 

 derable quantity. To separate the whole of this, we boiled 

 the wool several successive times in a mattras with weak 

 muriatic acid, but in order to lake up the last portions of 

 this acid 5 we were obliged to make use of such large quan- 

 tities of distilled water, that we were on the point of aban- 

 doning such tedious experiments, requiring so much time 

 and patience, as well as the greatest care. The separalioii 

 of all the muriatic acid from the first two hectogrammes of 



wool 



