In existographies, Jean Rey (1583-1645) was a French physician and chemist, noted for 
In 1630, Rey, in his Essay on Tying to Find out why Tin and Lead Increase Weight when Calcined, according to William Middleton (1964), was thinking about the weight and pressure of air. 
Rey, in this same work, according to Gilbert Lewis (1925), was the first person to clearly announce the law of the conservation of mass. 
Rey corresponded with Rene Descartes and Marin Mersenne.
Quotes | By
The following are quotes by Rey:
“Let there be taken a portion of earth which shall have in it the smallest possible weight, beyond which no weight can subsist: let this earth be converted into water by means known and practiced by nature; it is evident that this water will have weight, since all water must have it, and this weight will either be greater than that of the earth, or less than it, or else equal to it. My opponents will not say that it is greater, for they profess the contrary, and I also am of their opinion: smaller it cannot be, since we too the smallest weight that can exist: there remains then only the case that the two are equal, which I undertook to prove.”— Jean Rey (1630), The Increase in Weight of Tin and Lead on Calcination