SCIENTIFIC SUMMARY. 
453 
Crookes, F.R.S., has, however, devised a substitute for it in the shape oT a 
lamp, which meets nearly all the wants of the operation. A glass lamp is 
taken of about 2 ounces capacity, the aperture in the neck being 0-25 inch 
diameter; another aperture at the side allows the liquid fuel to be intro- 
duced, and by a well-known laboratory device, the level of the fluid in the 
lamp can be kept uniform. The wick-holder consists of a platinum tube 
1'81 inch long and 0T25 inch internal diameter. The bottom of this is 
closed with a flat plug of platinum, apertures being left in the sides to 
allow free access of spirit. A small platinum cup *5 inch diameter and T 
inch deep is soldered round the outside of the tube 0 5 inch from the top, 
answering the threefold purpose of keeping the wick-holder at a proper 
height in the lamp, preventing evaporation of the liquid, and keeping out 
dust. The wick consists of 52 pieces of hard-drawn platinum wire, each 
0-01 inch in diameter and 2 inches long, perfectly straight, and tightly 
pushed down into the platinum holder until only OT inch projects above 
the tube. The height of the burning fluid in the lamp must be sufficient to 
cover the bottom of the wick-holder : it answers best to keep it always at 
the uniform distance of 1'75 inch from the top of the platinum wick; a 
slight variation of level, however, has not been found to influence the light 
to an extent appreciable by our present means of photometry. The lamp 
having the reservoir of spirit thus arranged, the platinum wires parallel, and 
their projecting ends level, a light is applied, and the flame instantly 
appears, forming a perfectly-shaped cone 1*25 inch in height, the point of 
maximum brilliancy being 0‘56 inch from the top of the wick. The ex- 
tremity of the flame is perfectly sharp, without any tendency to smoke ; 
without flicker or movement of any kind, it burns, when protected from 
currents of air, at a uniform rate of 136 grains of liquid per hour. The 
temperature should be about 60° F., although moderate variations on either 
side exert no perceptible influence. Bearing in mind Dr. Frankland’s obser- 
vations on the direct increase in the light of a candle with the atmospheric 
pressure, accurate observations ought only to be taken at one height of the 
barometer. To avoid the inconvenience and delay which this w'ould occa- 
sion, a table of corrections should be constructed for each OT inch variation 
of barometric pressure. 
The Spectrum of Fotassium. — Mr. J. H. Freeman, in a communication to 
the Chemical Neivs (July 3), says, that of the seventeen lines which con- 
stitute the most characteristic part of the potassium spectrum, some make 
their appearance at a lower temperature than others. If a mixture ot 
10 eqs, of potassic nitrate, 10 eqs. of sulphur, and 3 eqs. of charcoal be 
ignited, and the light produced analysed by a spectroscope, it will be found 
that the double line at 130 on Bunsen and Kirchoif’s scale, the line at 430, 
the triple line at 1,120, and the line at 3,160 will be visible ; whilst the triple 
line at 1,300, the triple line at 1,500, the triple line at 1,760, and the line in 
the blue will be invisible. But if in the mixture we substitute potassic chlo- 
rate for the potassic nitrate, it will be found that all the lines, with the excep- 
tion of the one in the blue, will come into view. Butit is well known that the 
temperature produced during the combustion of KClOg and sulphur is much 
higher than the temperature of the combustion of KNO3 and sulphur; and 
a gradual increase of temperature from that produced by KNO3 and sulphur. 
