Test of the Potash. 275 



ample, which may contain | loth (-234 Troy ounce) water, 

 and measure with it any flask, in order to ascertain how 

 many of such measures it can hold ; 90 such measures are 

 now to be added, and 90 grans (86-3 grs.) of sulphuric acid 

 of the sp. gr. 1-850 accurately weighed out. Pour some 

 water out of the flask and agitate the sulphuric acid in it. 

 Wash the vessel well out with water sp as to lose no sul- 

 phuric acid, and then add this with as much water as will 

 again fill up the flask. 



Several loths (half-ounces) of the potash to be tested are 

 now to be well rubbed in a mortar, 10 grans (9 - 59 grs.) 

 weighed out, dissolved in a little water and mixed with 

 some tincture of litmus. When this is done, measures of the 

 above mentioned sulphuric acid test solution are to be 

 added gradually, until the blue solution of potash begins 

 to become red. If the red colour remains after the solution 

 is heated, it is a proof that all the alkali in the potash is 

 saturated with sulphuric acid, and the quantity of sulphuric 

 acid solution is now to be estimated. Since now each mea- 

 sure indicates a grain of sulphuric acid, so we calculate 

 according to the quantity of sulphuric acid employed, the 

 quantity of alkali contained in the potash, or what is the 

 same thing, the strength of the potash. Thus, 49 grans 

 (47- grs.) of sulphuric acid indicate 47| (45-5 grs.) of pure 

 potash.* 



A more convenient test of the potash for the dyer is this. 

 Several ellsf of cotton dyed chemical blue, j the process for 

 which will be subsequently described, are to be rolled up, 

 and laid uniformly together ; equally large pieces are then to 

 be cut out from it with a hollow chisel. A good specimen 

 of potash is then to be taken, and 1 gran (-959 gr.) dis- 

 solved in 300(287*7 grs.) pure water; heat the solution 

 in a porcelain basin over a spirit lamp, and put into it one 

 portion after another of the chemical blue cotton, in such 

 a manner that the first shall have lost its colour before 

 the succeeding one is introduced. At last a point will be 

 attained when the cotton will no longer be deprived of its 

 colour, but will retain its blue colour. 



* Or more correctly, 5 grs. sulphuric acid indicate 6 of caustic potash. — Edit. 

 t The f3erlin elle is equal to 666-9 millimetres or 2-188 English feet. — Edit. 

 t Records, vol. i. p. 823, 



t2 



