520 A FEW REMARKS OX BLEACHING POWDER. 



Moreover, as the processes used in estimating the strength of bleach- 

 ing powder bring the functions of the chlorine into play, much in the 

 same way as these are exercised in the act of bleaching, it is clear that 

 we have in these processes a complete index to the purity on the one 

 hand, or sophistication on the other, of any sample of bleaching 

 powder. 



The processes which have been recommended from time to time for 

 estimating the strength of chloride of lime, are nearly equal in point 

 of accuracy, but they are not all equally easy of performance. The 

 method which we would recommend the paper-maker to adopt is one 

 which, with a little care and nicety in its execution, may be employed 

 by almost any one, however little he may have been engaged in che- 

 mical pursuits. 



The only instruments that need be provided are a small common 

 balance which will turn with half a grain. The small beams and scales 

 used by the apothecaries will answer quite well. The other instru- 

 ment is a glass tube closed at one end and open at the other, this 

 open end having a small spout. It may be about eight inches long, 

 and nearly one inch in diameter, and should hold when rilled to near 

 its top, a little over two fluid ounces. There should be a mark about 

 an inch from the top, and the space between this mark and the bottom 

 should be divided into 100 equal divisions. Such graduated tubes may 

 be bought from almost any optician or philosophical instrument-maker, 

 at a small cost. 



The chemicals which are needed are very few, some tolerably clean 

 crystals of green vitriol (sulphate of iron), some solution of red prus- 

 siate of potash iferridcyanide of potassium), and some weak sulphuric 

 acid. 



Provided with these, we may now proceed to test the strength of 

 any sample of bleaching powder in the following way : — 78 grains of 

 the green vitriol crystals are weighed out and dissolved in water, to 

 which a drop or two of the weak sulphuric acid is subsequently added. 

 While this solution is making in a tumbler or cup, 50 grains of the 

 sample of bleaching powder are weighed out, and then thoroughly 

 stirred up and mixed with water (this is best done with a small 

 mortar and pi-stle), and then transferred to the graduated tube, and the 

 mortar or other vessel in which the mixture has been made, is now 

 washed, and the washings also added to the graduated tube until it is 

 filled up to O or zero. A few drops of the solution of the red prus- 

 siate of potash are now sprinkled on a common white plate. If the 

 crystals of srdphate of iron are now dissolved, then the mouth of the 

 graduated tube should be closed with the palm of the hand, and 

 its contents thoroughly shaken together, a creamy fluid being thus 

 formed. This mixed-up fluid should now be transferred little by little 

 to the vessel with the sulphate of iron solution. 30 or 40 measures 

 may be added at once, but after this the additions should be smaller. 



