PUM 



PUM 



in small bunches at the top of the stalks ; 

 calyx tubulous, hairy, as long as the tube 

 of the corolla ; brims of the petal spread 

 open, shaped like a cup, red, purple and 

 blue in tlie same bunch. Wocdville ob- 

 serves, that the name pulmonaria, seems 

 to have arisen rather from the speckled 

 appearance of the leaves, resembling that 

 of the lung-s, than from any intrinsic qua- 

 lity, which experience has discovered to 

 be useful iH pulmonary complaints. 



PULSE, in the animal ceconomy, de- 

 notes the beating or throbbing of the heart 

 and arteries. 



PULTENJEA, in botany, so named in 

 honour of William Pulteney, M, D. a ge- 

 nus of the Decandria Monog-ynia ciass 

 and order. Generic character: calyx, 

 five-toothed, with an appendage on each 

 side ; corolla, papilionaceous ; the wings 

 shorter than the standard ; legume of one 

 cell, with two seeds. There are six spe- 

 cies, all natives of New Holland. 



PULVERISATION, an operation, com- 

 monly employed in the apothecary's shop, 

 by means of pestles and mortars. The 

 bottom of the mortars should be concave ; 

 and their sides should neither be so in- 

 clined as not to allow the substances ope- 

 rated on to fall to the bottom between 

 each stroke of the pestle^ nor so perpen- 

 dicular as to collect it too much together, 

 and to retard the operation The mate- 

 rials of which the pestles and mortars are 

 formed, should resist both the mechanical 

 and chemical action of the substances for 

 which they are used. Wood, iron, mar- 

 ble, siliceous stones, porcelain and glass, 

 are all very properly employed ; but cop- 

 per, and metals containing copper, are to 

 be avoided, especially where the article 

 operated upon has a tendency to corrode 

 the metal. 



PUMICE, in mineralogy, is of a greyish 

 white colour : it occurs in mass and disse- 

 minated, being always more or less cari- 

 ous. It is glistening, with a silky lustre ; 

 its fracture is fibrous, its fragments are 

 sharp edged; it is opaque, sometimes a 

 little translucent on the edges ; it is ra- 

 ther soft, but its particles in powder are 

 very hard: it is fusible without addition 

 before the blow-pipe into a white enamel ; 

 it is regarded as a volcanic product, and 

 is wrought in considerable quarries in the 

 Lipari islands, which are almost entirely 

 composed of this mineral. It is found al- 

 so in Sicily and Iceland, It is composed 

 of 



Silica 77.5 



Alumina 17.5 



Oxide of iron 1.75 



Loss 



96.75 

 3.25 



100 



This mineral is employed in the arts for 

 grinding down metals, glass, ivory, &c. 

 previously to polishing. It is likewise 

 used in smoothing leather, and many 

 other purposes of the like kind. 



PUMP, in hydraulics, a machine form- 

 ed on the model of a syringe, for raising 

 of water. See HYDRAULICS 



PUMP air. See PNEUMATICS 



PUMP chain, consists of a long chain, 

 equipped with a sufficient number of 

 valves, at proper distances, which working 1 

 upon two wheels, one above and the other 

 below, passes downward through a wood- 

 en tube, and returns upward through 

 another. It is managed by a long winch or 

 roller, whereon several men may be em- 

 ployed at once, and thus it discharges, in 

 a limited time, a much greater quantity 

 of water than the common pump, and 

 with less fatigue and inconvenience to the 

 labourers. This machine was formerly 

 exposed to several disagreeable accidents, 

 by nature of its then construction. The 

 chain was of too complicated a fabric, 

 and the sprokel wheels, employed to wind 

 it up from the ship's bottom, were defi- 

 cient in a very material circumstance, viz. 

 some contrivance to prevent the chain 

 from sliding or jerking back upon the 

 surface of the wheel, which frequently 

 happened when the valves were charged 

 with a considerable weight of water, or 

 when the pump was violently worked. 

 The links were evidently too short, and the 

 unmechanical manner in which they were 

 connected exposed them to a great fric- 

 tion in passing round the wheels. Hence 

 they were sometimes apt to break or 

 burst asunder in very dangerous situa- 

 tions, when it was extremely difficult, 

 and sometimes impracticable to repair 

 the chain. Of late, however, some consi- 

 derable improvements have been made by 

 Mr. Cole, under the direction of Captain 

 Bentinck. The chain of this machine is 

 more simple and mechanical, and less ex- 

 posed to danger. It appears to have 

 been first applied to the pump by Mr. 

 Mylne, to exhaust the water from the 

 caissons at Blackfriar's Bridge. It was 

 thence transferred to the marine by Cap- 



