62 DR. R. ANGUS SMITH ON THE EXAMINATION 



and as the strength changes^ the amount of water to be 

 added will also change. If the amount of oxygen is given 

 as the result of the analysis instead of the amount of 

 chameleon solution, the strength of the latter does not 

 require to be kept uniform. The analyist requires only to 

 know its strength at the time of using it. For very bad 

 water, the strong solution may be used ; and when greater 

 delicacy is wanted it may be diluted. The weak solution 

 here used is made by adding nine of water to one of the 

 strong solution. 



" To make the chameleon solution, very pure water must 

 be employed, and very pure crystals, as well as very pure 

 vessels ; it is belter kept in considerable quantities, such 

 as a quart or two. It must be tried occasionally, say 

 every month, in a cool climate : calculation must be made 

 as allowance for any change which it may undergo. For 

 example, if it has lost I per cent., we must calculate how 

 much the number would have been had there been no loss 

 of strength. If calculation is not agreeable, a less quantitj^ 

 of solution may be made at a time, and that which is over 

 may be thrown away, a fresh amount being made to the 

 normal strength whenever the original weakens ; or a 

 certain amount of the crystals may be weighed and added 

 to the solution ; but this has been found less convenient. 



" The estimation of the value of the chameleon is some- 

 times made with a solution of chloride of iron, sometimes 

 oxalic acid. For ready reference, a Table is made showing 

 the amount of a solution of iron which corresponds to a 

 certain amount of chameleon. The sulphate of ammonia 

 and iron has proved to be very valuable, keeping for several 

 years in crystals, and acting instantaneously. The writer 

 has not found oxalic acid equally sharp and quick; but 

 eminent chemists use it — Mohr and Miller for example. 



