Mr. Crum on Testing Soltttiona of Bleaching Powder, 



six or eight parts of water it is quite colourless, but cliloride of lime 

 occasions with it the production of peracetate of iron, which has a 

 peculiarly intense red colour. 



A set of phials is procured, 12 in number, all of the same diameter. 

 A quantity of the proof solution, equal to ^th of their capacity, is 

 put into each, and then they are filled up with bleaching liquor of 

 various strengths, the first at y^gth of a degree of Twaddell, the second, 

 -^jths, the third, /^ths, and so on up to f fths, or 1 degree. They are 

 then well corked up, and ranged together, two and two, in a piece of 

 wood, in holes drilled to suit them. We have thus a series of phials, 

 showing the shades of colour which those various solutions are capable 

 of producing. To ascertain the strength of an unknown and partially 

 exhausted bleaching liquor, the proof solution of iron is put into a 

 phial similar to those in the instrument, up to a certain mark, ^th 

 of the whole. The phial is then filled up with the unknown bleach- 

 ing liquor, shaken, and placed beside that one in the instrument, 

 which most resembles it. The number of that phial is its strength in 

 12ths of a degree of the hydrometer; and, by inspecting the annexed 

 table, we find at once how much of a solution of bleaching powder, 

 which is always kept in stock, at a uniform strength of 6 degrees, is 

 necessary to raise the whole of the liquor in the steeping vessel to 

 the desired strength. 



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The instrument is formed of long 2 ounce phials cast in a mould ; 

 those of blown glass not being of uniform diameter. The outside, 

 which alone is rough, is polished by grinding, and in this state they 

 can easily be procured at 4s. 6d. a dozen. They are placed two and 

 two, so that the bottle containing the liquid to be examined may be 

 set by the side of any one in the series, and the colour compared 

 by looking through the liquid upon a broad piece of white paper 

 stretched upon a board behind the instrument. 



To explain the table it is necessary to state tliat the steeping vessels 

 we employ contain, at the proper height for receiving goods, 1440 

 gallons, or 288 measures of 5 gallons each, — a measure being the 

 quantity easily carried at a time. In the following table, represents 

 water, and the numbers 1, 2, 3, &c., are the strength of the liquor 

 already in the vessel in 12ths of a degree of Twaddell, as ascertained 

 by the chlorimeter. If the vessel has to be set anew, we see by the 

 first table that 32 measures of liquor at 6° must be added to (256 

 measures of) water to produce 288 measures of liquor at ^2*^^ 



