364 



ON MATERIALISiNI 



Hated, as it flows over a soil composed either wholly or in part of the earth 

 ealled magnesia ; it evinces a peculiar attraction for this substance, sepa- 

 rates it from the bed on which it has been quietly reposing, and so mi- 

 nutely dissolves it, as still to retain its transparency. But the attraction 

 of the sulphuric acid for the magnesia is much less than its attraction for 

 the fixed alkalis, potash and soda : and hence, if, to the water thus im- 

 pregnated, we add a certain quantity of either of the two latter substances, 

 the connexion between the acid and the magnesia will immediately cease : 

 the former will evince its perference for the alkali employed ; and the 

 magnesia no longer laid hold of by the sulphuric acid, will be precipitated, 

 or in other words, fall by its own weight to the bottom of the water in the 

 form of a white powder, and may be easily collected and dried. And this, 

 in reality, is the usual mode by which this valuable earth is obtained in its 

 pure state. 



But the sulphuric acid having thus shown a stronger attraction for an 

 alkah than for an earth, is there no substance for which it discovers a 

 stronger attraction than for an alkali ? There are various : it may be suf- 

 ficient to mention caloric or the matter of heat. And hence, exposed to 

 the action of heat, it soon becomes volatile, unites itself to the heat, flies 

 off" with it in vapour, and now leaves the alkali behind as it before left the 

 megnesian earth. Glass-manufacturers take advantage of this superior 

 attraction of the mineral acids for heat compered with their attraction for 

 alkalis, and employ, in their formation of glass, common sea-salt, which is 

 a combination of an acid and an alkali ; drive off" the former from the 

 latter by the aid of a very powerful fire, and then obtain a substance which 

 is absolutely necessary for the production of this material. 



These curious and altogether inexplicable properties and preferences 

 we call chemical affinities and chemical elections ; and there are nume^ 

 rous instances in which the substances, thus uniting themselves together, 

 evince an order and regularity of the most wonderful precision, and which 

 is nowhere exceeded, in the developement of the most elegant organ of 

 animated nature. And I now particularly aliudo to the phaenomena of 

 crystallization ; the different kinds of which, produced by the consolidation 

 <^f different substances, uniformly maintain so exact an arrangement in 

 the peculiar shape of the minute and central nucleus, or the two or three 

 elementary particles that first unite into a particular figure, and follow up 

 with so much nicety the same precise and geometrical arrangement through 

 every stage of their growth, that we are able, in all common cases, to dis* 

 tinguish one kind of crystal from another by its geometrical figure alone ; 

 and with the same ease and in the same manner as we distinguish one kind 

 of animal from another by its general m.ake or generic structure. The 

 form of these elementary particles we can no more trace to a certainty 

 than the bond of their union ; but there is great reason for believing them 

 to be spheres or spheroids, as first conjectured by that most acute and in^ 

 defatigable philosopher Dr. Hooke, and since attempted to be explained 

 by Dr. Wollaston in a late Bakerian lecture.* 



Such are the most striking powers that occur to us on a contemplation 

 of the unorganized world. From unorganized let us ascend to organized 

 nature. And here the first peculiar property that astonishes us is the prin- 

 ciple of life itself ; — that wonderful principle equally common to plants 

 3,nd ftnimals, which maintains the individuality, connects organ with organ, 



Phi!. Trans. 1813. |>. 51, 



