THEORY. 



anct3 could be drawn, he tlicn will be eotitled to (hare 

 ui the merit of the difcovery of tlie atomic theory. Wc 

 lay (hare with him, for wc are iinnly convinced that Mr. Dal- 

 ton had never read Mr. Higgins's book previous to the pub- 

 lication of his own work. 



We perfcftly recoileft the time, not more than four or 

 five years ago, even when Mr. Dahon's book was before 

 the public, vcr)' few chemills underllood the true fpirit of 

 the atomic theory ; and thofe who conceived they did under- 

 llaiid it, in general difcarded it. All knew that he con- 

 fidered compounds to be formed of atoms united i to i, 

 I to 2, I to 3, &c. : but it was not till the reciprocal 

 fitnefs of thefc atoms with each other was found to agree 

 with analyfis, that it was generally received. When they 

 faw that the numbers, whicli Dalton called tlie weights of 

 the atoms, expreffed tlie fimple proportions in which bodies 

 combine, they knew it could not be the effeft of chance, 

 and have willingly joined in the refearcli. It is for this 

 part of the difcover)- that Mr. Dalton juftly merits the 

 fame he has acquired. 



We have given all the fafts on which Mr. Higgins could 

 poflibly found liis claim to the difcovery ; and we muft 

 leave it to our readers to judge, whether they contain the 

 fmallell data on which to eftablilh what in the prefent time 

 wc call the atomic theory. 



In all the chemical articles fince the article Iron, we have 

 had the grcateft confidence in the atomic theory ; and we 

 have never failed to compare the analyfes of different autho- 

 rities with the refults given by theory. We have in general 

 found, that thefe refults have been nearer to the beft of thefe 

 authorities, than they have been to each other. 



We have already given an outline of the atomic theory, 

 with a table of the weights of the fimple atoms, and an- 

 other of fome of the moft confpicuous compounds, in our 

 articles Dcjinite Proportions, and Simple Bodies. 



The French chemifts have adopted the atomic theory 

 under another form, which will be found to agree with the 

 language given by Berzelius, who ufes the word •volume for 

 atom, as we have already explained in the article above al- 

 luded to. 



Gay Luffac feveral years ago publifhed a nevv- law refpeft- 

 iiig the combination of gafeous bodies. He held that gafes 

 which combine chemically, either unite in equal volumes, 

 or I to 2, or fome multiple of i, by a whole number. 

 Although a number of facls feemed to agree with this law, 

 the truth of it was doubted by fome chemifts, and princi- 

 pally becaufe no apparent reafon appeared for fuch a law. 



In ftating (under the article Proportions) the notion 

 of Berzehus refpefting volumes, we have pointed out a 

 curious coincidence between the fpecific gravity and the 

 weight of atoms of the gafes, which has fince been con- 

 finned by Dr. Prout in Dr. Thomfon's Annals. In order 

 that the weights of the atoms may be equal to their fpecific 

 gravities, we have there ftated, that the number of particles 

 in equal volumes of all gafes muft be equal, and tlic dif- 

 tance between the centres of the particles of all gafes the 

 fame, fo that the weights of equal volumes of different 

 gafes, would be as the weights of the atoms. 



This would alfo 'require, that the attraftion between the 

 particles ftiould either be the fame in all, or that it (hould 

 be nothing ; and the diftance of the particles be at points 

 where the repulfion of the calorific atmofphere is balanced 

 by the incumbent prclTure. 



The ftate hc-re fuppofed, however, is not the cafe, fince 

 we find tiiat the weights of the atoms of the gafes gene- 

 rally are not equal to the fpecific gravity, when reduced to 



the fame ftandard, although it is Itriclly the cafe with a 

 great proportion of them. And in thofe cafes where they arc 

 not equal, the one is faid to be fome multiple of the other, 

 by a whole number. 



This circumftance favours the hope that fome general 

 law exifts, by which the weights of the atoms of bodies are 

 intimately connefted with their fpecific gravities in the 

 elaftic form. When the fpecific gravity is double the weight 

 of the atom, as is the cafe with oxygen, we have to fup- 

 pofe, that the particles are nearer each other in the propor- 

 tion of 2 to 1, or that two particles come together, and 

 are furrounded by the caloric, which belongs to one o£ 

 them in tlieir fingle ftate. 



It would appear that the oxygen puts on this fingle ftate 

 of exiftence in the formation of carbonic oxyd, becaufe that 

 gafeous body contains only one atom of oxygen ; hence 

 its fpecific gravity is the fame as if it were formed from a 

 gafeous oxygen of half the real fpecific gravity united to 

 an atom of carbon without any change of volume, the fame 

 as takes place when fulphur or carbon is burned in oxygen 

 gas. Hence we may explain the gi-eat tendency that oxy- 

 gen has to combine in double dofes with bodies, as is the 

 cafe with carbon, fulphur, phofphorus, iron, and many 

 other bodies. 



We have alfo an inftance of a compound gafeous body be- 

 coming of double the fpecific gravity which would be ex- 

 pefted in olefacient gas, which is compofed of an atom of 

 carbon and an atom of hydi-ogen. The fpecific gravity 

 (hydrogen being i) ought to be i -(- 5.4 = 6.4; but 

 in faft it is about the double of this. Hence we fhould 

 conclude, that the repulfion between the particles is halved, 

 or that the compound atoms have united in pairs, by which 

 the denfity is doubled. 



Theory of the ManufaRwe and ProduB'ion of Bread, in 

 Rural Economy, the explanation of the principles and prac- 

 tices on which it depends in different cafes. The means which 

 are employed in fuch cafes are moftly well undcrilood ; but 

 the principles upon which they depend are far from being 

 fo well known. The writer of a late work on the " Ele- 

 ments of Agricultural Chemiftry," has, however, thrown 

 fome light on this hitherto intricate fubjeft. He has no- 

 ticed, that a number of the changes taking place in the 

 vegetable principles, depend upon the feparation of oxygen 

 and hydrogen as water from the compound ; but that there 

 is one of very great importance, in which a new combina- 

 tion of the elements of water is the principal operation : 

 this is in the manufafture of bread. When any kind of 

 flour, which confifts principally of ftarch, is made into a 

 pafte with water, and immediately and gradually heated to 

 about 440°, it increafes, it is faid, in weight, and is found 

 entirely altered in its properties ; it has loft its folubility in 

 water, and its power of being converted into fugar. In this 

 ftate it is unleavened bread. 



And when the flour of corn, or the ftarch of potatoes, 

 mixed with boiled roots of the fame kind, is made into a 

 pafte with water, kept warm, and fuffered to remain thirty 

 or forty hours, it ferments, carbonic acid gas is difengaged 

 from it, and it becomes filled with globules of elaftic fluid. 

 In this ilate it is raifed dough, and aff"ords by baking 

 leavened bread ; but this bread, it is faid, is four and dif- 

 agreeable to the tafte ; and that leavened bread for ufe is 

 made by mixing a little dough that has fermented, with new 

 dough, and kneading them together, or by kneading the 

 materials for the bread with a fmaU quantity of yeaft. 



It is ftated, that in the formation of wheaten bread, more 

 than one-fourth of the elements of water combine with the 



flour ; 



