USEFUL RECEIPTS The method now employed for producing " bleu de France," consists in boiling the wool in a bath containing ferridcyanide of potassium, an acid and chloride of tin, until a pure blue is produced. During this process a large amount of cyanogen is lost as hydrocyanic acid. To obviate this loss the process has been so modified as to precipitate the whole, or the greater part, of the cyanogen upon the fibres of the wool, in combination with iron. This object may be accomplished by adding a salt of iron to the bath, by preference the ses-quichloride. The dyeing is performed as follows :The ferridcyanide of potassium is first dissolved in the bath, then a small portion of the acid to be used, and fctiy the chloride of tin and iron. The liquid is now clear, and has a brownish color. The. wool, well washed, is put in while warm, and the bath heated to boiling. The wool at once takes a dark green color, and, after adding the remainder of the acid, becomes, on further boiling, a beautiful blue. In this manner, a given shade of color was produced with 25 per cent, less ferridcyanide than in the usual process. Experiments undertaken to ascertain the best proportions for adding chloride of iron, proved that the maximum effect was given by employing chloride equal to half or three-fourths the weight of the ferrocyanide. A larger amount gave a fainter color. The chloride was solution of iron in muriatic acid, through which chlorine has been passed. Less acid is here required than in the common process, and the tartaric proved most satisfactory. The ferridcyanide used must be perfectly free from ferrocyanide, oiherwise the addition of sesqui-chloride of iron would determine a precipitate of Prussian blue. [The above is from the " Notes by a Practical Chemist " in the " London Artisan." The author of said notes appears to be well posted up in applied chemistry, and often supplies very excellent articles. The article above is a description of a modification in dyeing the " Royal Blue,"old Prussian blue. The common method of dyeing this color, is to give about one ounce of the yellow prussiate of potash to one of wool, along with an ounce of tartar and one ounce of the chloride of tin. These substances are put into the dye kettle at lOOo dissolved, and then the wool is put in and the liquor brought up to 212" when the goods are taken out and about the same quantity of the chloride of tin added ; when the goods are again entered and the liquor brought to a boil, when the beautiful rich blue soon appears. Logwood added to the liquor makes a dark deep blue. Some recommend preparing the goods by boiling them first in a weak solution of the nitrate of iron, then washing well for the process described. In Prussia a patent is granted only f i six years, and it must be put in operation six monthsaf:er having teen granted.