Dr. Fyfe's Elements of Chemistry. 51 



judgement, Attraction was first treated of. Dr. Fyfe prefers the term 

 caloric to that of heat, observing that " by heat we are to understand 

 the sensation produced by a warm body j by caloric, the active cause 

 of this sensation." Having made this distinction between cause and 

 effect, our author proceeds to state, that " different bodies have dif- 

 ferent quantities [of caloric], and on this depends their temperature.' 

 This is an error of very considerable importance 5 and if one mistake 

 could be compensated for by another, Dr. F. has done all that can be 

 required of him, by asserting that " our sensations give us no indica- 

 tion whatever" of temperature j ergo, our sensations indicate no dif- 

 ference between a cold bath and a warm one. 



When treating of Pyrometers, Dr. F. has given a description of 

 Wedgwood's instrument, and on many occasions he refers to it as a 

 standard for determining the fusing-point of bodies ; and yet he ad- 

 mits the fact, ascertained we believe by Sir James Hall, that this py- 

 rometer is liable to one great objection, viz. that " if the clay be ex- 

 posed to a moderate heat for a long time, it will contract nearly as 

 much as if heated intensely." Being aware of this circumstance, all 

 notice of the instrument ought surely to have been omitted, for it is 

 worse than useless to quote that as authority which we do not believe 

 to be true. 



Under the head of Cohesive Attraction, some attention is naturally 

 bestowed by our author upon the subject of Crystallization. But the 

 little which he has said respecting it is so inaccurate and incomplete, 

 that it would have been better altogether omitted. No mention 

 whatever is made of a goniometer of any sort 5 and in treating of 

 Salts in the various parts of the work, their crystalline forms are very 

 erroneously described. Thus with respect to carbonate of soda, it is 

 stated that it crystallizes in octohedrons composed of two four-sided 

 pyramids joined by their bases j and Alum is correctly described as 

 possessing the octohedral form. We may therefore conclude that in 

 Dr. Fyfe's opinion there is no difference between the crystals of these 

 very different salts. The fact however is, that, although the apparent 

 form of carbonate of soda is an octohedron, yet it has a rhombic base 

 and it is elongated, whereas the octohedron of alum is a regular one. 

 We have said the apparent form is that of an octohedron, but this is 

 not the real form of the crystal ; Mr. Brooke has shown that it is an 

 oblique rhombic prism. Various other salts are very incorrectly de- 

 scribed, but we have not room for further observations on this subject. 



We are told by Dr. Fyfe, when treating of Acidifying and Alkalify- 

 ing principles, that the merit of the discovery of oxygen is due to 

 Priestley, Lavoisier, andScheele, the priority of it, only, being assigned 

 to Priestley. It is however quite clear from Dr. Priestley's statement, 

 (Doctrine of Phlogiston Established, p. 88. 1800.) that Lavoisier 

 knew nothing whatever of the existence of oxygen, until Dr. Priestley 

 mentioned it to him during a visit to Paris. On this subject there is 

 also another error, which we should not have expected in the work of 

 a medico-chemical writer. Dr. Fyfe says that Dr. Priestley procured 

 oxygen gas from red precipitate, whereas he particularly mentions 

 that he obtained it by employing mercurius calcinatus per se : this cir- 

 cumstance 



