Ow the nature of Lime, and other hinds of Cement. 



In order to difcover the reafon why Lime and Plaifter, being 

 moiftened with water, do, upon drying, acquire a degree of hard- 

 nefs like Hones, 1 took a piece of Limellone, which, by being burnt, 

 is rendered very foft, and divided it into very fmall particles ; thefe 

 I moirtened with pure rain water, and placed the mixture before the 

 microfcope : I did not at firft obferve it to undergo any alteration ; 

 but, continuing my eye fteadily and inceflantly fixed, both on the 

 fmaller and larger particles, I perceived, after ten or twelve minutes 

 had elapfed, a faint appearance of exceffively thin and minute faline 

 particles ; at the end of fifteen minutes I faw them very dillinclly ; 

 and in half an hour I faw, not only in every particle of the broken 

 Limeflone, but alfo in the water itlelf, fuch a multitude of faline par- 

 ticles as is almoft incredible. Thefe minute falts were not formed 

 in flraight lines, lying fide by fide, but for the mofl: part they crofled 

 each other in all directions. For example: I faw a particle of Lime- 

 flone lying diflinft by itfelf; this particle was more than a thoufand 

 times lefs than a grain of fand, and in it more than fourteen falts or 

 faline particles were formed; they were not all of the fame fize, 

 but fome larger than others, and alfo of different thicknefles ; but 

 the two longeft fides were all flraight, and parallel to each other ; 

 the two ends, or fliortefl fides, were obliquely fliaped, yet 

 parallel. This particle, with the falts which fliot or pro- 

 ceeded from it, as feen through the microfcope, are repre- 

 fented by the figure in the margin. 

 By the fight of this great quantity of falts lying together in this 

 irregular manner, and efpecially where the particles of Lime lay 



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