THAT ALL MATTER IS HEAVY. 201 



Then where this weightless element (as we may term it) is mixed with 

 weighty elements, we shall have a compound, in which the weight is no 

 longer proportional to the quantity of matter. If, for example, 2 measures of 

 heavy matter unite with 1 measure of phlogiston, the weight is as 2, and 

 the quantity of matter as 3. In all such cases, therefore, the weight ceases 

 to be the measure of the quantity of matter. And as the proportion of the 

 weighty and the weightless matter may vary in innumerable degrees in 

 such compounds, the weight affords no criterion at all of the quantity of 

 matter in them. And the smallest admixture of the weightless element is 

 sufficient to prevent the weight from being taken as the measure of the 

 quantity 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 supposition 

 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 possi- 

 bility 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 matter 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. 



Vol. VII. Part II. CC 



