VALUATION OP BLEACHING POWDER. 
277 
part of indigo dissolved in nine parts of sulphuric acid, and 
the whole diluted with 990 parts of water. 
In 1S24, Gay Lussac greatly improved upon the system 
of Decroizilles, and called the process for testing bleaching 
powders Chlorometry. 
His attention was chiefly directed to improvements in the 
method of producing the standard liquor, and in introducing 
apparatus of a simple construction, which, by their easy 
graduation and handling, rendered the process sufficiently 
easy for the practice of bleachers. 
Though this method is still employed by nearly all the 
bleachers on the Continent, it is subject to serious errors ; 
for instance, from the deterioration which the standard 
indigo liquor undergoes in time, and which consists in its 
gradual loss of strength. 
A second disadvantage, not less to be noticed, is a want 
of the knowledge of the exact time when the process is 
ended. 
It was owing to these principal difficulties, combined with 
some minor ones, that Gay Lussac was induced to search 
for some more accurate process, and after many years' trial 
he published, in 1S35, three new standard liquors, which 
shall be noticed after our attention has been directed for a 
short time to the system generally followed in this country. 
" It is one in which the chlorine is determined, by finding 
what quantity of the chloride of lime to be analysed is re- 
quired to convert a known weight of the protoxide of iron 
into peroxide. For this change protoxide of iron requires 
half an equivalent of oxygen, which is supplied in the pre- 
sent process by the decomposition of half an equivalent of 
water by the chlorine of the chloride of lime. 
" Half an equivalent of chlorine, therefore, or 221. S parts, 
effects this change upon a whole equivalent, or 439 parts of 
protoxide of iron, which quantity of protoxide is contained 
in one equivalent, or in 172S parts of crystallized protosul- 
phate of iron. Therefore, 221. S parts of chlorine can per- 
25 
