ON MINIMETRIC ANALYSIS. 203 



tion of test acid, and the equivalent for carbonic acid cal- 

 culated. The plan already described, with a ball from 

 which the manganate is pressed, suits the test very well 

 when the ball contains nothing which affects the salt. If 

 the ball is objected to, we may adopt another method. 

 This plan consists simply of a graduated tube like a pipette 

 fitted into the cork of the bottle j a small quantity is 

 allowed to flow down when required ; and when the liquid 

 begins to become purple, there being no more carbonic 

 acid to render it red, the experiment is finished : the amount 

 used is read on the graduated tube. 



At Mr. Hutchinson^s alkali works I obtained from Mr. 

 Powell a salt of ferric acid accidentally formed. It was 

 analyzed by Dr.Roscoe. This salt was expected to be still 

 more sensitive to organic matter than chameleon. It was 

 sensitive, certainly ; but it decomposed rather rapidly in the 

 light. It, however, can be used both for carbonic acid and 

 oxidizable matter, in the same manner as the manganate. 

 The action on light, however, is not quite suflicient to 

 make the salt a good photometer. The objection to it for 

 carbonic acid is that it does not keep well. 



The aspirator may be used for drawing the air through 

 any of these solutions, and either the ball apparatus or two 

 small bottles. Even one bottle may be used with great 

 safety, if it is covered from the air, and the speed not very 

 great; and by using Mr. Dancer's apparatus the exact 

 measurement of the air may be obtained. This proposal 

 appears like a . return to Dr. Reid's carbonometer, made 

 somewhat more convenient and elegant, and exactly quan- 

 titative. 



There may be varieties of tastes ; but I expect the first 

 and second methods to be very much used ; they are very 

 simple. It is quite possible to add many other methods 

 and modifications, but I know of none so simple as these. 



