268 Prof. WhewelVs Demonstration 



And the smallest admixture of the weightless element is sufficient to 

 prevent the weight from being taken as the measure of the qiaantity of 

 matter. 



" But on this hypothesis, how are we to distinguish such compounds 

 from bodies consisting purely of heavy matter ? How are we to satisfy 

 ourselves that there is not, in every body, some admixture, small or 

 great, of the weightless element ? If we call this element phlogiston, 

 how shall we know that the bodies with which we have to do are, any of 

 them, absolutely free from phlogiston ? 



" We cannot refer to the weight for any such assurance ; for by sup- 

 position the presence and absence of phlogiston makes no difference in 

 the weight. Nor can any other properties secure us at least from a 

 very small admixture ; for to assert that a mixture of 1 in 100 or 1 in 

 10 of phlogiston would always manifest itself in the properties of the 

 body, must be an arbitrary procedure, till we have proved this assertion 

 by experiment ; and we cannot do this till we have learnt some mode 

 of measuring the quantities of matter in bodies and parts of bodies ; 

 which is exactly what we question the possibility of, in the present 

 hypothesis. 



" Thus, if we assume the existence of an element, phlogiston, devoid 

 of weight, we cannot be sure that every body does not contain some 

 portion of this element ; while we see that if there be an admixture of 

 such an element, the weight is no longer any criterion of the quantity 

 of matter. And thus we have proved, that if there be any kind of mat- 

 ter which is not heavy, the weight can no longer avail us, in any case or 

 to any extent, as a measure of the quantity of matter. 



" I may remark, that the same conclusion is easily extended to the 

 case in which phlogiston is supposed to have absolute levity ; for in 

 that case, a certain mixture of phlogiston and of heavy matter would 

 have no weight, and might be substituted for phlogiston in the pre- 

 ceding reasoning. 



" I may remark also, that the same conclusion would follow by the 

 same reasoning, if any kind of matter, instead of being void of weight, 

 were heavy indeed, but not so heavy, in proportion to its quantity of 

 matter, as other kinds. 



" On all these hypotheses there would be no possibility of measuring 

 quantity of matter by weight at all, in any case, or to any extent. 



" But it may be urged, that we have not yet reduced the hypothesis 

 of matter without weight to a contradiction ; for that mathematicians 

 measure quantity of matter, not by weight, but by the other property, 

 of which we have spoken, inertia. 



