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so precipitate or fall to the bottom, and then the fluid n laid to be faturated with the body it has diffolved yet a fluid, which is faturated with one body, may afterwards difible. others of different kinds, and keep all their particles fulpended together. When any menftruum has entirely diffolved a body, it will continue as tranfparent as it was before. The caufe of which may be alligned from what Sir Ifaac Newton difcovered by experiments that the parti-

cles of bodies moil be of a ccrtain fae, or bignefs, to caufe any relleftion or refraftion of the rays of light at their furfaces. From whence he gives the rearms why fome bodies are opake, and others tranfparent and he alfo ohferves, that the moll opake bodies, filch as metals, being diffolved in an acid menfirunm, and thereby reduced to their ultimate and fmalleft particles, do not take away the tranfparency of the menlItuum. Hence we may always know how to dillinguifh a folution from a mixture for if a body be reduced to powder, and thrown into A fluid that will diffolve it, and they are then fhaken fuddenly together, the fluid will continue fomewhat opake till the folution be elFeEted, or till what remains undillifived falls to the bottom. For in this cafe the particles are not at firfi reduced to their fmalleft Ilse, as they are always in a folution. I think, therefore, we may confider the tranfparency of an heterogeneous fluid (or one that contains in it particles of another body) as the criterion of a true folution, and where that is wanting, it is only a mixture, as when water and air appear together in froth, or in a cloud, or a thick milt, it is only a mixture of chore bodies, and not a fulution

of either.

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