322 On the Common Blowpipe. 



or, which is more convenient, allow it to cool, then moisten it and 

 touch it to the substance which will immediately adhere. If the 

 same supports are to be used without fluxes then the trial piece may 

 easily be attached by a little adhesive clay, moistened. 



Pieces of glass tubes, about the diameter of a quill, and three or 

 four inches long, are often used with the blowpipe ; and are distin- 

 guished by the names " open tuhe'' or " matrass," according as the 

 tubes are open at both ends, or only one. They are often used to 

 roast substances ; or to expel from them some volatile substance 

 which may either condense on the cool part of the tube, or else by 

 its odor or some other characteristic property, be easily recognized. 



In tube experiments the spirit lamp is generally used ; for the 

 reason that although it gives less heat than the oil lamp or candle, 

 it possesses the advantage of not soiling the exterior of the tube. 



The fluxes generally used with the blowpipe are carbonate of 

 soda, biborate of soda, and the double phosphate of soda and am- 

 monia ; which for brevity are called " soda,^'' " borax," and " salt 

 of phosphorus." The last is also called microcosmic salt. 



Black flux may also be used advantageously in certain cases, but 

 a mixture of pounded charcoal with " soda" will supply its place. 



Soda or carbonate of soda, by uniting with silica aids the fusion 

 of refractory substances, and facilitates the reduction of metallic ox- 

 ides. It also, on account of the affinity of sodium for sulphur, ar- 

 senic, fee. often acts to reduce sulphurets, he. to the metallic state. 



Borax. — This substance also assists fusion on account of the 

 property it possesses of forming fusible salts with many substances 

 which themselves are infusible. By the color of the glass produ- 

 ced, the nature of the metal or metallic oxide is known. 



Salt of phosphorus. — When the substance is hekted it loses its 

 ammonia and is changed into a metaphosphate of soda, which unites 

 with bases and forms fusible salts, liberating the acids with which 

 the bases were combined. The characteristic colors of metallic sub- 

 stances are shown better with this substance than with borax. 



The following table, from Necker's " Regno Mineral" shows the 

 colors which various metals give with the three fluxes, when heated 

 either in the oxidizing or reducing flame ; and also shows the differ- 

 ence, if any, between the color of the glass when hot and when 

 cold. 



N. B. The letter H signifies hot glass, — C the cold glass. 



