Mr. Ceum on Testing Solutions of Bleaching Powder. 21 



On repeating the experiment in the way prescribed by Mr. Graham, 

 I find it of importance to mix the two solutions in a phial. It is 

 corked up and well shaken after each addition of the bleaching liquid. 

 By this means the cldorinc, a small quantity of which is set free after 

 every addition, is prevented from escaping, and a much more perfect 

 agitation and mixture is attained than by the use of the spatula. By 

 the same means the employment of the mortar and alkalimeter may 

 be dispensed with. If the 78 grains of the sulphate of iron bo put, 

 along with some muriatic acid, into a wide-mouthed 4 oz. phial, half 

 filled with water, the bleaching powder may be added dry, and the 

 result obtained by weighing the residue. 



Chlorimotry requires to be practised b^ the bleacher for two purposes 

 — First, he has to learn the commercial value of the bleaching powder 

 whicli ho purchases ; and with that view ho can scarcely desire any 

 thing better than the method either by arsenious acid, or green cop- 

 peras. But the more important, because the hourly testing of liis 

 bleaching liquor, and that on which the safety of his goods depends, is 

 the ascertaining the strength of the weak solutions in which the goods 

 have to be immersed. If the solution is too strong, the fabric is apt 

 to bo injured. If too weak, parts of the goods remain brown, and the 

 operation must bo repeated. The range within which cotton is safe in 

 this process is not very wide. A solution standing V on Twaddell's 

 hydi'ometer, (spec. grav. 1.005) is not more than safe for such goods, 

 while that of half a degree is scarcely sufficient for the first operation 

 of stout cloth, unless it is packed more loosely than usual. When the 

 vessel is first set with fresh solution of bleaching powder, there is 

 little difficulty, if the character of the powder be known ; but when 

 the goods are retired from the steeping vessels, they leave a portion of 

 bleaching liquor behind, unexhausted, which must be taken into 

 account in restoring the liquor to the requisite strength for the next 

 parcel. The chlorimeter must, therefore, be applied every time that 

 fresh goods are put into the liquid. It must consequently be intrusted 

 to persons who may not be expert either in figures or in chemical 

 manipulation. Hence all the processes I have described are too deli- 

 cate and tedious. 



I introduced another into our establishment some years ago, which 

 lias been in regular use ever since, and by which the testing is per- 

 formed in an instant It depends on the depth of colour of the per- 

 acetate of iron. A solution is formed of proto-chloride of iron, by 

 dissolving cast-iron turnings in muriatic acid, of half the usual 

 strength. To ensure perfect saturation, a large excess of iron is kept 

 for some time in contact with the solution at the heat of boiling water. 

 One measure of this solution, at 40" Twaddell, (spec. grav. 1.200) is 

 mixed with one of acetic acid, such as Tumbull and Co. of Glasgow 

 sell at 8s. a gallon. That forms the proof solution. If mixed with 



