1820.] Physical Science during the Year 1819. ' 2» 



common salt dissolved under like circumstances occasions a 

 dimiaution of temperature amounting only to 3*4°. A method of 

 idetermining Che relative proportion of these two salts whea 

 mixed together has been founded on this property, which, 

 from its extreme simplicity, deserves to fee known. The formula 

 will be simpler if we employ the centigrade thermometer : 204-® 

 of Fahrenheit is equal to 11-4'' centigrade, and 3*4° = \-^°. 

 The method of proceeding is this : Determine the degree of cold 

 produced diuring the solution of the salt, or the number of 

 degrees that the thermooneter sinks, let this be d. Then the 



quantity of muriate of potash in the mixture = — . 



The thermometei- ought to be delicate; the salt ought to be ia 

 the state of a fine powder, and the solution ought to be made as 

 rapidly as possible. The process is this : Weigh out 200 

 grammes of water, and determine its temperatra^e. Let as sup- 

 pose it 20'4°. Pour into the water as rapidly as possiWe 60 

 grammes of the salt previously reduced to powder. Hold the 

 vessel by the neck (a glass phial, for example), and agitate the 

 water, giving it a circular motion till the salt be dissolved. 

 Observe at what degree the thermometer stands at the end of 

 the solution, suppose it 12-8°. Then we have d — 20-4° — 

 12-8° = 7*6^ Of course the muriate of potash in 100 parts of 



the mixed salt is "^ " — = 60 very nearly. (Ann. de 



Chim. et de Phys. xii. 42.) 



8. Anhydrous Carbonate of Cop^er^ — In the Philosoplaacat 

 Transactions for 1813, I published the analysis of an anhydrous 

 -carbonate of copper from India. MM. Colin and Taillef«rt have 

 ascertained that when the green or blue carbonate of copper is 

 boiled in a quantity of water, it becomes otf a fine brown, in 

 consequence of the escape of its water. Thus they have disco- 

 vered the curious fact, that the hydrous carbonate of copper may 

 be rendered anhydrous simply by boiling it under water. The 

 brown powder which they thus formed is precisely Hke same as 

 the native anhydrous carbonate from India which I analyzed. 

 Thus all the three carbonates of copper may be made artificially. 



These gentlemen have ascertained likewise that the protoxide 

 of copper is capable of combining with carbonic acid, andforming 

 a yellow-coloured carbonate, wJaich is permanent in clos^e vessels, 

 but in the air gradually imbibes oxygen, and becomes brown. 

 (Ann. de Chim. et de Phys. xii. 62.) 



9. Acetate nf Lead. — In the Annals of Phihsophi/, xiv. 382, 

 I have given the properties and analysis of a new variety of 

 acetate oi" lead, which was accidentally formed in the sugar of 

 lead njanufactory of Charles Macintosh, Esq, of Glasgow. The 

 /:j-ystals were white and translucent, and nnich larger than those 

 Df conmion sugar of lead. They consisted of ihniuboidal prisms, 

 the plane angles of which measured 106° and 74°. Each prism 



