42 § 42. ANALYTICAL MAXIPULATIOX. 



too large, the division may be more accurately made by 

 weighing than by measuring. Get the weight first of the 

 whole amount of the liquid, in a small flask, pour out 

 about the quantity desired for a particular analysis, and 

 weigh the flask again with the remainder of the liquid ; 

 pour out another quantity and weigh again, and so on 

 until the division is completed. 



For this purpose, a flask with a little spout, attached 

 just below where the neck widens out into the body, will 

 be found very convenient. 



CALCULATION OF RESULTS. 



42t The results of an analysis are usually calculated so 

 as to give the per cent composition of the compound 

 analyzed. 



If the substance determined is weighed or estimated in 

 the form in which it existed in the compound, and it was 

 determined in the undivided solution of the same, noth- 

 ing remains to be done but to estimate the percentage by 

 a simple rale-of-three calculation, in which the amount 

 taken for analysis is the first term, the amount of the sub- 

 stance found the second, and 100 the third. 



If the substance was determined in a fractional part of 

 the f^olution, the same fractional part of tlic Aveight of the 

 compound taken for analysis must be made the first term 

 of the proportion ; or the amount of the substance found 

 may be estimated for the whole amount of the original 

 solution by multiplication by the proper number, and tliis 

 product is then made the second term of tlie proportion, 

 the first term being the weight of the whole amount taken 

 for analysis. 



In gravimetrical analysis the substance is usually 

 weighed in the form of some insoluble compound that 

 did not exist at all in the compound analyzed, and the 

 amount of the substance in the weight that was found of 

 this insoluble compound must first ba calculated. 



