Chloride of Lime. 287 



With iron alum, or with a solution of nitrate of iron, 

 prussiate of potash gives a dark blue precipitate, termed 

 Diesbach, or Paris blue. It is equally useful with the 

 preceding in block-printing, and when mixed with tartaric 

 acid and printed, it acts as a blue discharge for madder- 

 purple. With copper salts this salt gives a brownish-red 

 colour which does not withstand soap. It is equally good, 

 and more valuable to prepare it with catechu and chips 

 of mahogany. 



Chr ornate of potash. — There are a yellow and a red chro- 

 mate of potash. The yellow is employed to produce chrome- 

 orange, and the red to form chrome-yellow. 



When an acid is added to the yellow-chromate of potash 

 it is converted into the red. If one is only in possession of 

 the yellow-chromate of potash, it may readily be converted 

 into the red and into yellow colours by the addition of an 

 acid. For this purpose, nitric acid is employed. Upon 99 

 lbs. yellow-chromate of potash, pour 60 lbs. nitric acid of 

 the specific gravity 1 # 288. 



As an acid converts the yellow chromate of potash into 

 the red, so on the other hand, an alkali changes the red 

 into the yellow. A clear solution of potash is here very 

 proper. Crystallized carbonate of soda may be employed 

 for the same purpose. To 151 lbs. of red-chromate of 

 potash add 143 lbs. crystallized carbonate of soda. 



The red-chromate of potash is but little liable to adultera- 

 tion, the yellow is more so. The most correct test for the 

 dyer, is the quantity and quality of its dyeing power. The 

 proportion given under chrome colours, affords a standard 

 forjudging of the goodness of a chrome salt. 



Chloride of lime as it occurs in commerce is of very dif- 

 ferent strengths. As it consists of chlorine and lime, and 

 is in the form of a dry powder, it must necessarily contain 

 an excess of lime, and is easily adulterated by means of 

 lime. As this excess of lime separates by solution in water, 

 the value of the chloride of lime may be estimated accord- 

 ing to the quantity which remains undissolved, when the 

 dissolved part is chloride of lime. This may also be 

 muriate of lime and the like. 



Good chloride of lime must be dry and a little trans- 

 lucent, must bake together and produce no dust on being 



