8 History of physical Science from [July, 



These data are scarcely sufficient to determine the point in 

 question, as several of the numbers, both indicating the specific 

 gravity and the proportion of oxygen, are unquestionably inac- 

 curate. Were the law to hold good, it would indicate the 

 existence of a certain relation between the density of the metals 

 and the weight of their atoms — a relation which may possibly 

 hold, though the present state of our knowledge does not enable 

 us to perceive it. Such researches are, perhaps, rather prema- 

 ture. We ought in the first place to determine the composition 

 of the metallic oxides with absolute precision. The relation 

 between the oxides and the specific gravity, if any such exists, 

 will then present itself to our view. 



III. ANALYTICAL IMPROVEMENTS. 



1. On the Mode of separating Lime from Magnesia by the 

 Bicarbonate of Potash. — Bucholz dissolved equal weights of 

 lime and magnesia in muriatic acid, and precipitated by adding 

 a solution of bicarbonate of potash to the liquid. At first no 

 precipitate whatever fell, or at least the precipitate was imme- 

 diately redissolved by agitating the liquid. After a certain 

 interval, a portion of the lime was separated in the state of 

 carbonate ; but he was unable, by this method, to separate the 

 whole, or nearly the whole, of that earth. When the proportion 

 of magnesia held in solution was small compared with that of 

 the hme, in that case a much greater proportion of the lime was 

 thrown down by the bicarbonate; but even in this case the 

 whole of the lime was not thrown down. Bucholz concludes 

 from these experiments that this method does not succeed, and 

 that it ought not, therefore, to be practised. — (Schweigger's 

 Journal, xvii. 56.) 



According to Dbbereiner, the best method of separating lime 

 from magnesia is to employ the carbonate of ammonia. The 

 lime in that case falls while the magnesia remains in solution 

 forming a triple salt with the ammonia. The magnesia may be 

 afterwards precipitated by boiling the liquid which contains it. 

 -(Ibid. p. 78.) S H 



2. Neto Method of detecting Arsenic and Corrosive Sublimate. 

 — Brugnatelli has proposed the following method of detecting 

 these poisonous substances. Take a quantity of fresh wheat 

 starch, mix it with water, and add a sufficient quantity of iodine 

 to give the liquid a lively blue colour. When an aqueous solu- 

 tion of white arsenic is let fall into this liquid, the blue colour 

 disappears, and it becomes reddish. The same change is brought 

 about by a solution of corrosive sublimate. A few drops of 

 sulphuric acid will restore the blue colour, if it has been de- 

 stroyed by arsenic ; but it will not restore it if it has been 

 destroyed by corrosive sublimate.— (Ann. de Chim. et Phys. 

 iv. 334 ; and Annals of Philosophy for May, 1818.) 



IV. GASEOUS -BODIES. 



1. Escape of compressed Gases through capillary Tubes. — It 



