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In the year 1841； while practicing the art in St。 Louis； Mo。； I was at times； during the summer； much troubled with the electric influence of the atmosphere； especially on the approach of a thunder…storm。 At such times I found the coating of my plates much more sensitive than when the atmosphere was comparatively free from the electric fluid； and the effect was so irregular that no calculation could counteract the difficulty。 This satisfied me that electricity was in some measure an important agent in the chemical process； and it occurred to me that the element might be turned to advantage。 I determined； therefore； to enter on a series of experiments to test my theory。 Finding it impossible to obtain an electric machine； and unwilling to abandon the examination； it occurred to me； that the galvanic influence might answer the same purpose。 I therefore proceeded to make a galvanic battery in the following simple manner。 I obtained a piece of zinc about two inches long； one inch wide； and an eighth of an inch thick。 On this I soldered a narrow strip of copper； about six inches long； the soldered end laid on one side of the zinc； and extending its whole length。 The battery was completed by placing the zinc in a glass tumbler； two…thirds full of dilute sulphuric acid； strong enough to produce a free action of the metals。 The upper end of the copper slip extending above the tumbler was sharpened to a point； and bent a little over the glass。
The method of using； was thus：After preparing the plate in the usual manner and placing it in the camera； in such manner as to expose the back of the plate to view； the battery was prepared by placing the zinc in the acid； and as soon as the galvanic fluid began to traverse （as could be known by the effervessence of the acid； operating on the zinc and copper） the cap of the camera was removed； and the plate exposed to the sitter； at the same instant the point of the battery was brought quickly against the back of the plate； and the cap replaced instantly。 If the plate is exposed more than an instant after the contact the picture will generally be found solarized。 By this process I have taken pictures of persons in the act of walking； and in taking the pictures of infants and young children I found it very useful。 Very respectfully yours； THOMAS R。 WHITNEY。
CHAP。 VII
PAPER DAGUERREOTYPES。ETCHING DAGUERREOTYPES。
Mr。 Hunt describes a process； discovered by himself by which the Daguerrean art may be applied to paper。 His description is as follows：
〃Placing the paper on some hard body； wash it over on one side by means of a very soft camel's hair pencilwith a solution of sixty grains of bromide of potassium； in two fluid ounces of distilled water； and then dry it quickly by the fire。 Being dry； it is again washed over with the same solution； and dried as before。 A solution of nitrate of silver one hundred grains to an ounce of distilled wateris to be applied over the same surface； and the paper quickly dried in the dark。 In this state the papers may be kept for use。
〃When they are required； the above solution of silver is to be plentifully applied； and the paper placed wet in the camera； the greatest care being taken that no day light not even the faintest gleamfalls upon it until the moment when you are prepared； by removing the dark slide； to permit the light； radiating from the object you wish to copy； to act in producing the picture。 After a few seconds the light must be again shut off； and the camera removed into a dark room。〃 The necessity of removing the camera is now avoided by the use of the dark slide； already described； covering the picture in the holder； which alone may be removed。Amer。 Aut。
〃It will be found by taking the paper from the holder； that there is but a very faint outlineif anyyet visible。 Place it aside； in perfect darkness until quite dry； then place it in the mercurial vapor box （meaning bath） and apply a very gentle heat to the bottom。 The moment the mercury vaporizes； the picture will begin to develope itself。 The spirit lamp must now be removed for a short time； and when the action of the mercury appears to cease； it is to be very carefully applied again； until a well defined picture is visible。 The vaporization must then be suddenly stopped； and the photograph removed from the box。 The drawing will then be very beautiful and distinct； but much detail is still clouded； for the developement of which it is only necessary to place it in the dark and suffer it to remain undisturbed for some hours。 There is now an inexpressible charm about the pictures； equaling the delicate beauty of the daguerreotype； but being very susceptible of change； it must be viewed by the light of a taper only。 The nitrate of silver must now be removed from the paper； by well washing it in soft water； to which a small quantity of salt has been added； and it should afterwards be soaked in water only。 When the picture has been dried； wash it quickly over with a soft brush dipped in a warm solution of hyposulphite of soda； and then wash it for some time in distilled water； in order that all the hyposulphite may be removed。 The drawing is now fixed and we may use it to procure positive copies； （the original being termed a negative；） many of which may be taken from one original。〃
〃The action of light on this preparation； does indeed appear to be instantaneous。 The exquisite delicacy of this preparation may be imagined； when I state that in five seconds in the camera； I have； during sunshine； obtained perfect pictures； and that when the sky is overcast； one minute is quite sufficient to produce a most decided effect。〃
〃This very beautiful process is not without its difficulties； and the author cannot promise that； even with the closest attention to the above directions； annoying failures will not occur。 It often happens that some accidental circumstancegenerally a projecting film or a little dustwill occasion the mercurial vapor to act with great energy on one part of the paper； and blacken it before the other portions are at all effected。 Again； the mercury will sometimes accumulate along the lines made by the brush； and give a streaky appearance to the picture； although these lines are not at all evident before the mercurial vapor was applied。 （A brush sufficiently largeand they may be easily obtained will； in a measure； prevent this difficulty。Amer Au。） I have stated that the paper should be placed wet in the camera； the same paper may be used dry； which often is a great convenience。 When in the dry state a little longer exposure is required； and instead of taking a picture in four or five seconds； two or three minutes are necessary。〃
The durability of daguerreotypes has been； and is still； doubted by many； but experiment has proved that they are more permanent than oil paintings or engravings。
ETCHING DAGUERREOTYPES。There are several methods of accomplishing this object； discovered and applied by different individuals。
The first process was published at Vienna by Dr。 Berres； and consisted in covering the plate with the mucilage of gum arabic； and then immersing the plate in nitric acid of different strengths。
Mr。 Figeau； of whom I have already spoken； likewise discovered a process for the engraving of Daguerreotypes； and founded on the belief that the lights of a Daguerreotype plate consists of unaltered silver； while the dark or shadows consists of mercury or an amalgam of mercury with silver。 He finds that a compound acid； consisting of a mixture of nitric； nitrous； and muriatic acids； or of nitric mixed with nitrate of potass and common salt； has the property of attaching the silver in presence of the mercury without acting upon the latter。 Bi…chloride of copper answers the purpose also； but less completely。
〃When the clean surface of a Daguerreotype plate is exposed to the action of this menstruum； particularly if warm； the white parts； or lights are not altered； but the dark parts are attacked； and chloride of silver is formed； of which an insoluable coating is soon deposited； and the action of the acid soon ceases。 This coat of chloride of silver is removed by a solution of ammonia； and then the acid applied again； and so on； until the depth of biting in is sufficient。 However； it is not possible； by repeating this process； to get a sufficient force of impression； a second operation is required； in order to obtain such a depth as will hold the ink； to give a dark impression； for this purpose the whole plate is covered with drying oil； this is cleared off with the hand； exactly in the way a copper plate printer cleans his plate。 The oil is thus left in the sinkings； or dark bitten in parts only。 The whole plate is now placed in a suitable apparatus； and the lights or prominent parts of the face are gilt by the electrotype process。 The whole surface is now touched with what the French engravers call the 〃Resin Grain；〃 （grain de resine）； a species of partial stopping out； and it is at once bitten in to a sufficient depth with nitric acid； the gilding preserving the lights from all action of the acid。 The resin grain gives a surface to the corroded parts suitable for holding the ink； and the plate is now finished and fit to give impressions resemb