Replies to Papers o?i various Electrical Subjects, ^55 



mixtuft over a water-bath. The first was digested in a well- 

 closed vessel durin<r fourteen days: but no greater combining 

 proportion of water was observed than in the second speci- 

 men, which was only digested for twenty-four hours. — I have 

 procured a similar result by merely moistening the earth, and 

 immediately drying it over the water-bath. The combination 

 is immediate, and, as has been shown, admits of no increase in 

 the proportion of water by a prolonged digestion. If boiling 

 water be used in forming the hydrate, no difference is ob- 

 served in its constitution. It may be remarked how nearly 

 the first analysis approaches to the proportions of atom to 

 atom, for assuming 20*7 as the atomic weight of magnesia, we 



^»^v^' Magnesia 20*7^ 



Water ^ 9*02 



It seems certain from these experiments, that magnesia is 

 capable of combining with water in one proportion only. 



The precipitate obtained by the addition of ammonia to » 

 neutral solution of sulphate of magnesia approaches also very 

 nearly in constitution to a protohydrate of the earth, i found 

 100 parts of the precipitate (well dried over a water-bath) to 



yi^'^ Magnesia 66*7 



Water 33*3 100. 



LXXXVII. Replies by Mr. E. M. Clarke, the Rev. Professor 

 Callan, a7id Dr. Ritchie to certain Papers on Subjects of 

 Electricittj and Magneto-electricity inserted in the preceding 

 and present Volumes of the Philosophical Magazine. 



npHE following is the substance of communications which 

 ^ we have received from the gentleman above named. We 

 have omitted nothing which could tend to elucidate the sub- 

 jects under discussion : indeed the reply of the Rev. Professor 

 Callan to Dr. Ritchie, and that of the latter to the Rev. J. W. 

 MacGauley, are inserted almost entire. 



Reply of Mi\ E. M. Clarke ^o Mr. J. Saxton,(See vol.ix. p.360). 



" I proceed to rq^ly to Mr. SaxUm's remarks one by ane.> 

 In the first place I have not laid claim to the electro- 

 magnetic machine (as he ealls ii): as my invention, but I have 

 certainly termedj a magnetic electrical machine E. M. Clarke's, 

 owing to a material difference having been made in its cow- 

 struction, the advantages arising from which I shall now pro- 

 ceed to point out. First, it will readily be admitted that vi- 

 bration tends to injure the magnets. In Mr. Saxton's machine 

 very great vibration is unavoidable, in as much as all the ma- 



