VOL. LXX.] P^HILOSOPHICAL TRANSACTIONS. til 1 



them, we may try to make a precipitation with the metal which is lowest but one 

 in the order of elective attractions, and so proceed to the next above it, till we 

 come to the highest; and by this means we shall obtain all the metals in the 

 mass. There are other principles on which Dr. F. founded various processes for 

 assaying; but these are sufficient for copper ores, all the different known 

 species of which he actually assayed, and therefore ventured to offer this process 

 to the consideration of the r.s ; 1'. as only requiring an apparatus which can 

 be bought at any apothecary's or chemist's, and as capable of being performed by 

 a person totally unacquainted with chemistry, so that any proprietor of an 

 estate, or his servant, may determine if an ore be of copper, and its value; 

 2°. as affording an assay-master a more perfect manner of determining the value 

 of a copper ore; and lastly, as a process by which the naturalist may investigate 

 not only the copper in an ore, but its various other contents. There is but one 

 known species of copper ore in which the copper is not capable of being com- 

 bined with aqua regia, which is blue vitriol, which is sometimes found solid, but 

 more frequently in mineral waters; from this tlie copper may be precipitated by 

 iron immediately. 



Many opinions, (Dr. F. remarks) have been published of metals being found 

 in mineral waters combined with various substances. He never examined any 

 mineral water in which he found the metals combined with any other substance 

 but vitriolic acid; and he was certain, many authors had been misled b« not 

 knowing this property of metallic salts, viz. that if we dissolve them in a small 

 proportion of water, or if there be superfluous acid, the solution will remain 

 perfect when exposed to the air; but if the acid be perfectly saturated with the 

 metal, and the proportion of water to the metallic salt be very great, on exposure 

 to the air it is decomposed, the metal precipitating in the form of a calx, and 

 the acid being lost. This may easily be tried by taking common green or blue 

 vitriol, dissolving 1 oz. in 3 oz. of water by boiling, letting them stand to cool, 

 and filtering the solution. If this solution be exposed to the air it will remain 

 perfect; but if we drop a drop or 2 of it into a wine glass full of water, in a few 

 minutes the transparency of the water will begin to be disturbed, and the metal 

 in a short time will fall down, in a red powder if it be of iron, in a blue powder 

 if it be copper. A hundred grains of the ore is sufficient to give the copper 

 contained to -pio- part; if greater accuracy be required, lOOOgrs. may be used. 



The mixture of nitrous and muriatic acid is the most proper acid menstruum 

 for copper ores, muriatic acid dissolving most readily the calces of metals, and 

 nitrous acid when they are in their metallic form; a metal in its metallic form 

 being a compound of a pure calx and a substance, which has been called inflam- 

 mable air, but which is an oil found out by Stahl to exist in metals, and which 



4 I 2 



