2 <; 2 THE POPULAR SCIENCE MONTHLY. 



by tin and lead when they are calcined. " Now/' he said, " that 

 I have made my preparations, that is, have laid the foundations 

 of my answer to his question " (as to the source of the seven 

 ounces which the two pounds and six ounces of tin gained when 

 heated for six hours ; the difficulty of the problem was en- 

 hanced by its being necessary also to find the other matter 

 required to compensate for the loss which the tin sustained 

 through expansion in heating): "to this question, then, resting 

 on the formulations already laid, I answer and maintain glori- 

 ously, that the increase in weight comes from the air, which has 

 been thickened in the 'vessel, made heavy, and in no way adhe- 

 sive, by the vehement and long-continued heat of the furnace ; 

 which air mingles with the earth (the frequent stirring aiding 

 this) and attaches itself to the smallest particles ; not otherwise 

 than water makes sand heavy when sand is wet and the mass is 

 stirred, by moistening and adhering to its smallest grains/' 



Several authors had already spoken of the increase of weight 

 in metals on calcination. Cardan, in his Traite' de la Subtilite*, 

 tried to explain the increase of the weight of lead in the forma- 

 tion of white lead by saying it was because the lead died and lost 

 the celestial heat which was its soul and made it lighter; and 

 added that an animal is always heavier dead than living. Rey 

 remarked, in answer to this, that lead is void of life and can not 

 be compared with the body of an animal, and showed that it was 

 easy, by a known process, to recover the lead from its earth. 

 Further, " nothing increases in weight except by the addition of 

 matter or by contraction of volume," and this can not take place 

 in the present case, even under Cardan's hypothesis, for the celes- 

 tial heat in disappearing takes away matter, while on the other 

 hand the volume increases perceptibly through the whole dura- 

 tion of the experiment. It will be noticed that Rey shared in the 

 prejudice of his time in regard to the weight of animals increas- 

 ing after their death, and with him many of the learned men of 

 the period. Pere Mersenne was the first to refute this error. He 

 ascertained by experiment that a dog and a hen weigh more, 

 though very little more, alive than dead, and wrote to Jean Rey, 

 September 1, 1631, " You can yourself try the experiment with- 

 out losing any of the blood, or a hair, or a feather, of the animals, 

 by smothering them, as we have done." 



Scaliger had undertaken to refute Cardan's assertions, and 

 said that the increase in the weight of the calcined lead was 

 caused by the fire consuming its aerated particles, comparing lead 

 with the Jtile, " which is heavier baked than unburned." Noth- 

 ing could be more simple than Rey's answer : " If the lead loses 

 airy particles, would it not diminish in volume ? On the contrary, 

 it increases. And then, if this reason is correct, why do not 



