SIE B. C. BEODIE ON THE CALCULUS OF CHEMICAL OPERATIONS. 791 



point under consideration, those properties which had varied would he of fundamental 

 importance ; but as for most purposes these variations may be disregarded the object is 

 still assumed to be the same, and called by the same name, a gramme of water. Let 

 the temperature rise to 100°, and let a new observation be made. The liquid has 

 become a gas, and the change of properties is so great that a new name is assigned to 

 the portion of matter, and it is said that the gramme of water has been converted into 

 a gramme of steam. Nevertheless, many of the properties of the steam are identical 

 with those of the water, and these being the properties with which the chemist is 

 mainly concerned, he asserts the identity of the two objects for the purposes of his 

 science, and says, notwithstanding this transformation, that steam is simply the gaseous 

 form of water. Now let the conditions be again varied. At a further elevation of 

 temperature it vdll be found that a more profound change has occurred. In the place 

 of one continuous portion of matter, in every part of which the same properties may be 

 recognized, wo have two distinct chemical substances, each characterized by a special 

 set of properties. The volume has permanently altered; many chemical as well as 

 physical properties of the water have entirely disappeared. The chemist marks this 

 change by assigning a new name to the portion of matter, and says that the water has 

 been converted into oxygen and hydrogen. It has, however, been found that even in 

 this profound change one property has not been affected, namely, weight. This property 

 is constant ; and we assert in the most absolute sense that the weight of a gramme of 

 water is identical with the weight of the gramme of oxygen and hydrogen into which it 

 is transformed, for this property, throughout this series of changes, has never varied 

 nor ceased to have a continuous existence. Now a gramme of water will produce the 

 same effect on a balance as a gramme of lead, and it is this relation which is here 

 termed equality of weight. This relation also subsists between the weight of a gramme 

 of water and the weight of the gi-amme of oxygen and hydrogen into which it is trans- 

 formed ; but these weights are also connected by another relation, which I have termed 

 identity, which does not exist between the gramme of water and the gramme of lead. 



It is thus that we are led by experience to the inference comprised in the following 

 statement. 



If a portion of matter A be chemically converted into a portion of matter Aj, then 

 the weights (or portions of matter considered as regards weight) of which A consists are 

 identical with the weights (or portions of matter considered as regards weight) of which 

 Aj consists. 



It will be found, on analyzing the process of reasoning by which we conclude the con- 

 tinuous existence of the same Aveight in a chemical change, that the evidence by which 

 it is supported is precisely of the same order as that by which we are enabled to assert 

 the continuous existence of any external object whatever. This evidence is brought 

 spontaneously and without effort before the mind, and is so perfectly conclusive, however 

 difficult it may be to submit it to analysis, that an eminent writer has actually imagined 

 the doctrine of the permanence of weight in chemical changes to be a truth which 



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