GASEOUS SPECTRA UNDER HIGH DISPERSION. 459 



I confess require the greatest personal thought and attention. — I aru, dear Sir, yours very 

 truly, Charles F. Casella. 



P.S. — Your note of the 31st just to hand. I will carry out your suggestion by using 

 naked copper wires instead of gutta-percha covered ones, which already are suspended across 

 my laboratory with a pair of leads coming down to each Pump. 



Before doing so, however, may I have your opinion on the following suggestion in 

 opposition to yours, namely, the various strong and damp fumes the naked wires would be 

 subjected to, would create a strong oxidation on them, and would not therefore the current, 

 instead of conveying one gas into the tubes, which gas we already are acquainted with, carry a 

 variety of " gaseous " all sorts into our tubes. 



This is a mere hypothesis of mine, and therefore please take it for what it is worth. 



C. F. C. 



London, E.G., 13th Nov. 1883. 



Dear Sir, — Your favour of the 9th inst. has duly reached me, and I have now much 

 pleasure in telling you that I am back again in office, having returned last week. 



Before being able to say that I am ready to commence vacuum tube work again, I must 

 tell you that my pump room or laboratory is without pumps, they having all become spoilt and 

 broken by wear and tear. 



To make fresh ones will take about two or three weeks, they being very elaborate but 

 exquisite instruments. 



Please state how many olefiant and acetylene tubes and at what pressure you would like. 



I will note all my chemical proceedings, and also let you have an account of those last 

 sent, which is as follows, viz.: — Action of Nitric Acid on pure copper filings (turnings), gas 

 collected in a receiver in water, and communication from receiver to pump, the gas first 

 passing through four drying tubes as follows, viz. — (1) Chloride Calcium, (2) Anhydride 

 Phosphoric Acid, (3) Anhydride Phosphoric Acid, (4) Caustic Potash. Minor details, &c, 

 were conducted as before, but with the same care in every respect. — Yours truly, 



Charles F. Casella. 



Previous to these chemical operations of Mr C. F. Casella, his father, Mr Louis P. 

 Casella, had had some curious experiences with the wires forming the electrodes of his vacuum 

 tubes. 



Platinum wires usually blacked the inside of the bulbs ; wherefore he then tried gold, — 

 the following recommendation of that metal in the Proceedings of the Eoyal Society, London 

 (and subsequently reprinted in the Philosophical Transactions, Part I., for 1884, page 51), 

 having been brought to his notice : — 



" Of all metals affording materials for electrodes, gold appears to be the best ; its spectrum 

 is a weak one, containing comparatively few lines ; it is an excellent conductor of electricity, 

 and it is not attacked by solutions of metallic chlorides." 



No sooner, however, did he try this highly commended material than the iusides of his 

 tubes were brilliantly, opakely, and utterly gilt by it, combined with the six-inch induction 

 sparks employed. He had, therefore, to fall back on aluminium wire and to use that very 

 thick, or between ^ and ^ inch in diameter. C. P. S. 



VOL. XXXII. PART III. 4 E 



