CHEMICAL SCIENCE. 



nip or carrot 4,480 pounds, and pass them through a crushing machine, 

 or otherwise reduce them to a high degree of pulverization, and throw 

 them into a heap upon a suitable floor in a warm room, stirring the mass 

 once a day for three weeks, or until fermentation has taken place through- 

 out the whole. Next add a pint and a half of alkali (or of a combination 

 of fifteen parts of lime to one of sal-ammoniac) to every two hundred 

 pounds of the material, and thoroughly incorporate it with it, stirring 

 it over occasionally until the acid fermentation has become neutralized. 

 The compound is then fit for use, but improves by age. Patent Office 

 Report for 1848. 



A SIMPLE AND CERTAIN TEST OF THE QUALITY OF INDIGO. 



REINSCH tried various modes of determining the goodness of indigo, 

 but none of them gave results to be relied on till " at last," he says, " I 

 resorted to fuming sulphuric acid, and obtained the most satisfactory 

 results. It is necessary, however, that the indigo should be pounded 

 very fine, and the acid should be as concentrated as possible. The 

 mode in which I proceed is as follows : One tenth of a gram* of each 

 sample of indigo is well pounded, mixed with four or five drops of 

 fuming sulphuric acid, and rubbed with it till the whole forms a brown 

 uniform mass. To this one gram of sulphuric acid is added, and tritu- 

 rated till it produces a clear green solution, whereupon another gram of 

 fuming sulphuric acid is added ; lastly, this solution is gradually mixed 

 with ten grams of water. Two glass cylinders of equal width and 

 length are now divided each into twenty equal parts, and one gram of 

 the sulphuric solution poured into one and mixed with water, till the 

 solution is of a light blue color and transparent; if one gram of the 

 solution does not produce sufficient coloration, a small quantity more of 

 it is added, till the cylinder is filled with the light blue solution. I 

 generally commence with the apparently best indigo. After this, the 

 second cylinder is filled in the same way with an equal quantity of the 

 same indigo sample and water, in order to see whether the two solutions 

 are equal in color. If this be the case, one of the cylinders is emptied, 

 and an equal quantity of sulphuric acid solution of an inferior sample 

 poured into it, and gradually diluted with water, till the solutions in 

 both cylinders are perfectly alike in color. Care must be taken to have 

 both solutions of exactly the same hue, and as soon as this is accom- 

 plished, the quantity of water which has been poured into the second 

 cylinder is examined. Supposing now that one gram of sulphuric acid 

 solution has been employed in both of the cylinders, but the quantity 

 of water which produced the equal color was in the first or standard 

 cylinder twenty parts, and in the second only fifteen parts, then the 

 sample of which the latter solution was made will contain one quarter 

 less of coloring matter. For some reason the Java indigo and that 

 chemically prepared by treating it with acid, caustic potash, &c., do not 

 give the desired results, and I therefore used Bengal, first quality, which 

 excelled all others in coloring capacity, and contained at least fifty per 

 cent, pure coloring matter. 



* A gram equals nearly 15 grains Troy. 



