216 The Art of Dyeing. 



This easy solubility affords a ready method of separating it 

 from tartar, with which it may be adulterated, and which 

 is very little soluble in water. If a solution of 1 lb of tartaric 

 acid in 2 lbs. water, thickened with gum, be printed on cot- 

 ton, and allowed to hang for 14 to 21 days at a temperature 

 of 15° R (65°-J) to 21° (79°i), we shall find that the printed 

 places have suffered no injury, but are as strong as the un- 

 printed portions. The printed specimen has, as at the be- 

 ginning, a sharp border. Tartaric acid does not corrode the 

 cotton, and attracts no moisture from the air, which would 

 moisten it and produce a border. A strong heat in drying 

 is injurious. 



These properties render tartaric acid an excellent mor- 

 dant, especially in the Turkey-red or purple manufacture. 



A solution of nitrate of lead may be mixed in the solution 

 of tartaric acid, without decomposition following. Hence, 

 this forms a mordant of chrome-yellow upon madder-purple. 



Tartaric acid decomposes chloride of lime by precipitating 

 the lime and setting the chlorine free, which exhibits its 

 bleaching action. Tartaric acid is, therefore, printed on a 

 madder ground and dipped in a solution of chloride of lime ; 

 the printed parts become white, while the unprinted parts 

 remain red. 



The tartaric acid combines readily with potash, and forms 

 tartar, or takes up a portion of potash from the sulphate of 

 potash, forming tartar and bi-sulphate of potash. This last 

 salt is very corrosive, and destroys the cotton like sulphuric 

 acid ; this fact deserves attention, and points out to the 

 dyer, the rule never to bring tartaric acid and sulphate of 

 potash together. This may sometimes happen without his 

 knowledge, as in mixing Berlin or Paris blue not suffi- 

 ciently edulcorated with tartaric acid, or in mixing tartar 

 with sulphuric acid. In the last case, there is formed, not 

 common sulphate of potash, which is not injurious, but bi- 

 sulphate of potash. 



Oxalic and citric acids. — Oxalic acid occurs in commerce 

 in white crystals, which, if they are pure when held over a 

 spirit lamp in a silver spoon, are completely dissipated. If 

 a drop of oxalic acid falls upon cotton impregnated with 

 the iron mordant, a rust yellow colour is produced, and a 

 white spot remains upon the place. If this spot is allowed 



