File:A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14783309422).jpg

Identifier: manualofpractica00turn (find matches)
Title: A manual of practical medical electricity : the Röntgen rays and Finsen light
Year: 1902 (1900s)
Authors: Turner, Dawson
Subjects: X-Rays Electrophysiology Electrosurgery Electric Stimulation Therapy Electrotherapeutics X-rays Electrophysiology Electrosurgery
Publisher: New York : William Wood & Company
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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current ofmore than twelve amperes strength. Two of this size, connected in parallel, serve in my ownhands to bring a short platinum cautery to a white heat.Eight to ten of the smallest size connected in series willbring a laryngoscopic lamp to full incandescence, and, ifin parallel, will heat for a very short period a cautery. Further, the cell is exceedingly portable ; containing noliquid, it cannot be upset. Failure owing to evaporation,or to short-circuiting through creeping of salts outside thevessel, cannot occur. There is no action when the cell is notin use ; the zincs have not to be lowered when the currentis required, to be raised again immediately afterwards. The small cells measure i^ x i;- x 3I inches, and weigheight ounces each. All forms of dry cells are modifica- 46 A Manual of Practical Medical Electricity tions of Leclanche cells, and none of them are as durableand reliable as the ordinary form of wet cell. Whethercurrent is drawn from them or not, they slowly become
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useless, mainly owing to an increase in their internalresistance. Double Fluid Cells. The only really constant cells are the two liquid ones,and of these the Daniell is the most important. Forms of Primary Cells 47 (a) The electrolyte is a dilute (i to 20 or 40) solutionof sulphuric acid, usually contained in a porous pot. (b) The positive plate is of zinc, which lies in theexcitant solution. (c) The negative plate is of copper. (d) The depolarizer is a saturated solution of sulphateof copper. The E. M. F. is roughly equivalent to one volt. Theinternal resistance is somewhat high, varying from abouttwo to ten or more ohms, according to the size and formof the cell. The chemical changes are very simple. The zinc dis-solves during action in the excitant solution to form zincsulphate, while hydrogen is set free ; the latter, appearingat the junction of the two liquids, displaces the copperfrom its solution to form sulphuric acid and metalliccopper ; the acid passes back to the zinc, and

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