484 FRANKINCENSE 



furnace is filled, to diminish the facility of the discharge, and consequently to 

 retard the efflux by the nozzles. The oxygen gas consumed is replaced by a like 

 volume of carbonic acid gas, equally expansible by heat. Reason leads us to conclude 

 that less air flows from the nozzles into the furnace than into the open atmosphere. 



The increase in the velocity of the vanes takes place precisely in the same manner, 

 when after having made the nozzles blow into the atmosphere, we substitute for these 

 nozzles others of a smaller diameter, instead of directing the larger ones into the fur- 

 nace. Hence we may conceive that the proximity of the charged furnace acts upon 

 the blast like the contraction of the nozzles. When the moving power is uniform, 

 and the velocity of the vanes remains the same, the quantity of air discharged must 

 also bo the same in the two cases. 



Two tuyeres, one 5 inches in diameter, the other 4, and which, consequently, pre- 

 sented a total area of 35 square inches, discharged air into one of the furnaces, from a 

 fan whose vanes performed 654 turns in the minute. These two nozzles being briskly 

 withdrawn from the furnace, and turned round to the free air, while a truncated paste- 

 board cone of 3 inches diameter was substituted for the nozzle of 4 inches, wherein 

 the area of efflux was reduced to29'3 square inches, the velocity of the vanes continued 

 exactly the same. The inverse operation having been performed, that is to say, the 

 two original nozzles having been smartly replaced in tke furnace, to discover whether 

 or not the moving power had changed in the interval of the experiment, they betrayed 

 no perceptible alteration of speed. From the measures taken to count the speed, the 

 error could not exceed three revolutions per minute, which is altogether unimportant 

 upon the number 654. 



It follows, therefore, that when the vanes of the fan have the velocity of 654 turns 

 per minute, the expenditure by two nozzles, whose joint area is 35 square inches, 

 both blowing into a furnace, is to the expenditure which takes place, when the same 

 nozzles blow into the air, as 35'5 is to 29 '3 ; that is, a little more than ths. 



If this be, as is probable, a general rule for areas and speeds considerably different 

 from the above, to find the quantity of air blown into one or more furnaces by the fan, 

 we should calculate the volume by one of the above formulse (1) or (2), and take 

 fths of the result as the true quantity. 



The fan A c, represented (fig. 1003), is of the best excentric form, as constructed by 

 Messrs. Braithwaite and Ericsson. D is the circular orifice round the axis by which 

 the air is admitted ; and c c B is the excentric channel through which the air is 

 wafted towards the main discharge pipe E. See VENTILATION. 



FOUNTAIN. A stream of water rising through the superficial strata. 



FOWLER'S SOLUTION. A solution of arsenite of potash used in pharmacy. 



FOXGLOVE. The Digitalis purpurca, a common British plant, belonging to the 

 natural order Scrophulariacece. The leaves and other parts contain a poisonous prin- 

 ciple called digitaline. In small doses foxglove is used as a diuretic and for lessening 

 the action of the heart, but in larger doses it altogether stops the circulation. 

 The vulgar name foxglove is said to be a corruption of folKs-glove (fairy's glove), in 

 allusion to the shape of the flower. 



FOXING, is a term employed by brewers to characterise the souring of beer, in 

 the process of its fermentation or ripening. 



FRACTIONAL DISTILLATION. A process of distillation, in which, by 

 regulating the heat, fluids possessing different degrees of volatility are separated from 

 earn other. See NAPHTHA, BOGHEAD. 



FRACTURE OP MINERALS. The fracture of minerals has been grouped 

 under the following heads, there being very few variations from them : 



1. Conchoidal; from concha, like a shell, when a mineral breaks with curved con- 

 cavities ; example, flint. 



2. Even; when the surface of fracture is not rough, and has no small elevations 

 and depressions. 



3. Splintery ; when the broken surface exhibits protruding points. 



4. Hackly ; when the elevations are sharp or jagged, as iron. 

 FRAME, a mining term. See DRESSING OF ORES. 

 FRANCOLITE. A variety of apatite. See APATITE. 



FRANGULIN. A yellow crystalline substance obtained, from the bark of the 

 HJiamn us frangula. 



FRANKFORT BLACK is a black used in copper-plate printing. It is said 

 to be a charcoal obtained from grape and vine lees, peach kernels, and bone shavings. 

 It is doubtful whether the finest, black is not a Boot produced from the combustion of 

 some of these bodies. The preparation is, however, made much of a m\ - 



FRANKINCENSE. The spontaneous exudations of the Abies cxcelsa, the Norway 

 spruce fir. East Indian frankincense is said to be derived from certain species of 



