ON MINIMETttIC ANALYSIS. 197 



carried out with the lime than with the baryta-water. 

 Lime-water may be prepared of the same constant strength 

 so closely that we may neglect the difference ; with baryta 

 we are apt to make the solution unnecessarily strong, and 

 so waste it; but the experiment will still be the same. 

 Lime-water is common; but baryta-water could also be 

 prepared cheap, if there were a demand for it. 



The use of this method would enable us to distinguish air 

 in this manner : — We could say. This is 6-ounce air, that 

 is 4-ounce air, that is 2-ounc6 air (meaning that 6, 4, or 2 

 ounces of it cause a precipitate in baryta- water) ; and any 

 person would understand it, and prove it easily ; whilst 

 vials, so often seen in cottages, might be converted into 

 scientific instruments for sanitary purposes. 



ind. For all amounts of Carbonic Acid, the bulk of air 

 varying. — If it be desired to ascertain the amount of car- 

 bonic acid in air of which we know nothing, the following 

 less simple apparatus is proposed : — 



An elastic india-rubber ball may be made to contain any 

 given amount ; let us suppose two ounces. When we press 

 it in the hand we can drive out the whole air, or at least 

 nearly the whole ; we let it go, and it fills again. If a tube 

 be fitted to it we can drive the air which has gone into 

 the ball through baryta- or lime-water, and obtain the 

 precipitate before spoken of at the beginning. It is 

 preferable, however, to cause the air to pass through the 

 baryta- or lime-water before entering the ball ; and this 

 can easily be done. If the air be pure, it will require 

 so many more balls to be emptied ; if impure, a srqaller 

 number. 



If a ball with a simple tube is used for blowing into a 

 liquid, that liquid is drawn up as soon as the ball expands,, 

 and many fillings cannot be made without inconvenience. 

 If, however, a valve be placed between the liquid and the 

 ball, there can be no return. This is the case in the tube 



