or Linen Cloths capable of resisting teaching, &c. g 



saponaceous leys, but because in drying slowly they run, 

 and very oi'ten occasion spots. 



If those composed with spirit-varnish were even not 

 attended with the inconveniences of speedy evaporation and 

 desiccation, still it would be as improper to employ them 

 as the preceding, because, turpentines and resins are verv 

 easily transformed into soap. Nor can gum -copal be used 

 for colours for marking, because it is detached from the 

 stuff by mere ebullition iu water. 



By employing oil of turpentine, which evaporates and 

 dries less speedily than alcohol, I have succeeded in obtain- 

 ing a black composition, which to me appeared capable of 

 being; used with advantage for marking cloths. It is made 

 by dissolving slowly in oil of turpentine,, in a sand-bath, 

 continually stirring it, a quarter of its weight of asphal- 

 tum, or bitumen of Judea, broken into small pieces, and 

 afterwards mixing with it as much- as possible of lamp- 

 black, or black produced by any mineral substance what- 

 ever, highly coloured, and in very fine powder; cither car- 

 buret of iron, sulphuret of lead, or any other. The colour 

 will be obtained more or less thick according to the pro- 

 portions of the oil of turpentine and bitumen ; it will mark 

 exceedingly well without running, observing the just pro- 

 portions, and diluting it with a new portion of oil of tur- 

 pentine, if while it is in use it acquires too much consist- 

 ency. This bituminous colour bears equally well the action 

 of alkaline leys and of oxygen, and resists all acids of a 

 certain strength. 



Finding it unnecessary to continue the trials of oily co- 

 lours, I undertook the aqueous experiments in the follow- 

 ing order : 



Exp. I. I dissolved in four ounces of water one ounce of 

 Sulphate of manganese, deprived of its water of crystalliza- 

 tion, such a.-; is obtained by procuring the oxygen gas of the 

 black oxide of manganese, by means of sulphuric acid, and 

 by increasing the violence of the fire towards the conclusion 

 of the operation, so as to ignite the retort. This solution 

 vvas'lhickened with a dram of fine gum-dragon in powder, 

 and coloured with lamp-blacTc, to render t!ie accuracy of 

 the impressicm more visible, which is executed very easily 

 with this black, saline, metallic mass, of which, how- 

 ever, no use can be made, excepting the ends of the 

 marked cloths be plunged into alkaline ley, without pre- 

 viously passing it through water, to take away the salino 

 matters. The ley may be made with potash or soda, in 

 the proportion of one part of alkali to from nine to twelve, 

 parts oi water : it may be used in the state of carbonate, or 

 ^ lendcred 



