94 O^^ THE SIGNIFICATION OF CHEMICAL TERMS. 



Dr Thonnon Dr. Thbmsort, in a sliort essay on affinity in general, uses 

 •n a puj. the term ^ar/jc/tf frequently, and without any direct <lefini- 

 tion ; but jas he advances his idea of particle is gradually 

 ^developed. Indeed lie is almost the otdy writer, who has 

 .courage to talk of a particle, two particles, &c. Homage' 

 neous particles are those of the same body ; heterogeneous 

 particles those of different bodies; thus ** a particle of iron 

 and a particle of lead are heterogeneous." Again, ** on 

 integrant particle of water is composed of particles of hi- 

 jdrogen and oxigen urged towards each other, and kept at 

 ^ an insensH)le distance, by heterogeneous affinity; and a 



rnass of water is composted of an indefinite number of inte- 

 grant particles of that fluid, urged towards each other by 

 homogeneous affinity." lie supposes the particles of mut- 

 ter to have figure and magnitude, and adds, " if the parti- 

 cles of bodies have length, breadth, and thickr*ess, we 

 cannot avoid conceiving the»n as composed of an indetermi- 

 nate number of still more minute particles or atoms. Now 

 the affinity of two integrant particles for eaelv other must 

 be the sum of the attractions of all the atom§ in each of 

 these particles for all the atoms in the other,'* .^e. .Here 

 the meaning of a particle is very clearly pointed out. Bo- 

 dies, such as iron, are constituted of particles connected 

 together by homogeneous affinity ; these particles are each 

 nf them constituted of a certain unknown number of sub- 

 ordinate particles, which last are the atoms or ultimate par* 

 tides, into which the body is capable of being resolved 

 without decomposition. Thii notion is cleiir as far as it 

 goes {I mtai) not as to its truth, but as to the expression) ; 

 it would seem however to require something to be said aboijit 

 the cohesion of the atoms to form a particle, namely, whe* 

 ther it is the same or ditferent from the cohesion of the pur- 

 tic! ep to form a muss; in other words, whether the force of 

 cohesion, which binds togjcther the atoms or ijrst ,or4er of 

 particles, is the same as that which binds the second order 

 of paiticle«. See Thomson's Chemistry, 3d ed. vol. iii. 

 M array^s Che- M r. Murray uses the term particles frequeutly ; he com- 

 nuhtry. mences Kis work wiih the observation, that *' all the pheno- 



mena of chemistry arise from the attractions auti repulsions 

 exerted be^tweeu the particle* of inutter;'' bwt 1 have: not 



• -}t 



been 



