210 The Art of Dyeing. 



as it is free from foreign matter. Next to it comes rain and 

 river water ; but spring water does not answer for dyeing, 

 because it contains a quantity of lime, which falls down 

 with the colouring matter in the form of an insoluble 

 precipitate, and thus occasions great loss of colouring 

 matter. The same happens when well water is employed 

 for boiling dye-woods and roots. When the reddish yellow- 

 coloured Dutch madder is boiled with pure water, the re- 

 sidue, after drying, acquires a light brown colour, and im- 

 parts to a solution of alum a faint red colour when both are 

 boiled together. When, on the other hand, spring water is 

 substituted, the residue is dark reddish brown, and the so- 

 lution of alum, by being boiled with it, becomes dark red. 

 In the first case, the quantity of madder-red remaining in 

 the residue is much less than in the second. The madder- 

 red has been precipitated by the lime of the spring water, 

 and has imparted to the residue the dark colour, and is 

 dissolved by the alum solution. Pure water, therefore, 

 dissolves more madder-red than water containing lime 

 does. 



With Fernambuc and logwood the same results are 

 obtained. 



To determine whether river water is fitted for dyeing, the 

 above experiment may be had recourse to, or a specimen 

 may be dyed, first with the water to be tested, and then 

 with pure distilled water. 



The presence of lime may also be detected in such waters 

 by chemical means. When soap is added to water con- 

 taining lime, and the mixture heated, it becomes turbid. 

 Carbonate of soda makes it milky, and throws down a white 

 precipitate. Oxalate of potash acts in a similar manner.* 



Water which flows over marshy ground often contains in 

 solution a quantity of decomposed vegetable matter, which 

 especially acts upon oiled cotton and soils it. Such water 

 is likewise injurious to the white ground. Chrome colours 

 especially chrome-yellow lose their lustre and become ugly. 

 This proceeds principally from the sulphur contained in 



* Oxalate of ammonia answers better than this salt, because the precipitate can 

 be readily freed from alkali by heat ; while, if oxalate of potash is employed, the 

 precipitate requires to be thoroughly washed, (and this is difficult to effect), before 

 ignition. — Edit. 



