NATURE 



[May 3, 1894 



various means that have been proposed and used for 

 producing the deposit are then shown, and drawings are 

 given for an apparatus for " coal gas flashing " at atmo- 

 spheric pressure. It is, however, recommended that the 

 pressure should be reduced, as otherwise there is danger 

 of getting a soft deposit. A detailed description is next 

 given with drawings of an apparatus for flashing in 

 "pentane" vapour at reduced pressure. Different 

 methods for flashing filaments to a uniform resistance or 

 candle-power are described, and it is noted that the 

 specific resistance of hard white carbon deposited from 

 pentane is one-tenth that of carbon deposited from 

 amyloid. Several pages are given to a consideration of 

 the best thickness for the deposited carbon, and a curve 

 diagram is given, showing the erfect of reduction of re- 

 sistance due to flashing for filaments of various diameters. 



In chapter vi. are given useful formula for finding the 

 sizes for filaments for lamps of various candle-powers, 

 with either round, flat, square, or tubular filaments , based 

 on the data obtained from amyloid carbon with un- 

 polished surface. In connection with tubular filaments, 

 the fallacy of supposing them to be more economical than 

 the solid form " because all the power is used in heating 

 the surface," is explained. 



Chapter vii. gives the sizes necessary for the produc- 

 tion of lamps of various candle-powers, using flashed 

 filaments. This is far more difficult than in the case of 

 unflashed carbons, and instead of giving the cumbrous 

 formula necessary, a number of different cases are work ed 

 out separately, and the results given in a series of curves 

 from which the sizes for any other candle-power can be 

 quickly obtained. At the conclusion of this chipter, the 

 author alludes to a very amusing instance of what he calls 

 the " happy-go-lucky " method of working that he en- 

 countered in a factory some few years ago. The name 

 of the works in question is not divulged, and as he speaks 

 of it being in a country where "very badly matched 

 lamps " could be sold as of the same voltage, we hope 

 England is not responsible. We thoroughly endorse his 

 opinion that the most carefully made lamos.even though 

 the price may be higher, will prove the cheapest in the 

 end. This is a point in the manufacture of lamps which 

 deserves more attention than is usually given to it, and a 

 thorough grasp of the contents of these chapters will be 

 of great value to anyone intending to take up the subject 

 seriously. The aim of the manufacturer should be to 

 turn out the most perfect lamp possible, and one in whic h 

 the limit of endurance has been attained. Practice will 

 then reduce the cost of production. 



Chapter viii. contains a brief description of various 

 gauges used for measuring the diameters of filaments. 

 Although it is not mentioned, we should think the beau- 

 tiful little instrument used for measuring the thickness of 

 microscopic cover glasses would answer the purpose 

 admirably. 



A chapter is devoted to glass-making, including a list 

 of ingredients necessary for the manufacture of lead 

 glass, the kind of pots for melting the '' metal " in, and a 

 short description of the method of blowing " pot-bulbs " 

 in a mould. Glass-blowing is fully gone into, and, after 

 describing the playful way in which the old-fashioned 

 orthodox glass-blowers "spoiled " the electricians in the 

 early days of lampmaking, we come to the invention of 



NO. 1279, VOL. 50] 



the glass-blowing machine, and the final springing into 

 existence of a race of girl glass-blowers free from the \ 

 vices of drink, strikes, and " Saint Monday." 



We then have a few pages with illustrations showing 

 the various forms of blowpipes, ending with practical 

 instructions for making lamp bulbs from glass cylinders. 

 This is given somewhat briefly, doubtless owing to the 

 fact that it is pretty evident that the day is not far distant 

 when this method of forming bulbs will entirely give 

 place to the quicker and more suitable method of " pot- 

 blowing.' 



Chapter xi. is headed '' Sealing in," andcontains some 

 good drawings and descriptions of the methods used for- 

 fixing the filaments in the glass bulb. The small anneal- 

 ing oven to stand on the workman's bench, and receive 

 the lamps as they are finished, is a very useful piece of 

 apparatus, and is a great advance upon the old method 

 of holding the work in a smoky flame, a practice 

 which is not only dirty, but wastes both time and gas. 



Touching upon glass grinding and the manufacture of 

 taps, it is remarked that good taps can be bought cheaply 

 made of German glass, but there is very great difficulty 

 in joining them to the lead glass used in the exhausting 

 apparatus. It is not generally known that this can be 

 easily and effectually done by interposing between the 

 German and the lead glass a thin stratum of soft white 

 enamel or " arsenic " glass, used as a solder. Compound 

 joints made in this way are perfectly sound, and are not 

 at all liable to crack. 



The important subject of exhausting is treated of in 

 chapter xii. and it is pointed out that to produce a good 

 lamp a high vacuum is absolutely necessary. The reasons 

 against leaving a residual atmosphere of nitrogen or 

 other inert gas are discussed, and then follows a com- 

 plete description of the various forms of mercurial 

 pumps in use. Several kinds of short-legged pumps are 

 shown and described in detail. The " Sprengel pump" 

 does not hold the prominent place it occupied some years 

 ago, preference being given to the various forms of 

 Geissler pump. The reason for this may lie in the great 

 number of india-rubber joints that appear to be used. 

 This way of making pumps always gives constant 

 trouble through leakage, and poor efficiency is unavoid- 

 able. We cannot agree with the author that india-rubbi"^ 

 joints are to be allowed. There is no doubt that ind 

 rubber joints are almost universal in modern lamp fac- 

 tories, but we have equally little doubt that the short life 

 of many of the lamps now on the market is due to im 

 perfect exhaustion; and having had considerable r 

 perience in high vacua, we have no hesitation in saym 

 that a vacuum sufficiently good for a long-lived inc.u; 

 descent lamp can only be obtained if all the joints arc 

 hermetically sealed together. We have still in use 

 lamps dating from iS,S2 exhausted properly with sealed 

 joints, and they have outlived generations of bought 

 lamps made with 'he use of india-rubber joints. 



For testing the vacuum the McLeod gauge is noted, but 

 is not considered to be of much use to the lamp-maker. 

 The size of the bubble in the chamber of the " Geissler,'' 

 and the appearance and " hammer " of the mercury in 

 the legs of the " Sprengel," are taken as sufficiently good 

 indications for the purpose. This certainly savours of 

 the "rough and ready" method, but in the absence of 



