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tion and instantly removed。 There is another point； too； in the preparation of the iodized paper in which suggestions for a slight deviation from Mr。 Talbot's plan have been made。 In the first instance； it is recommended that the paper be brushed over with the iodide of potassium； instead of the nitrate of silver； transposing； in fact； the application of the first two solutions。 The paper； having been brushed over with the iodide of potassium in solution； is washed in distilled water and dried。 It is then brushed over with nitrate of silver； and after drying is dipped for； a moment in a fresh solution of iodide of potassium of only one…fourth the strength of the first； that is to say； one hundred and twenty…five grains of the salt to a pint of water。 After this it is again washed and dried。 The advantage derived from this method； is a more sensitive paper； and a more even distribution of the compounds over the surface。
Another deviation from Mr。 Talbot's method has been suggested； as follows：
Brush the paper over with a solution of one hundred grains of nitrate of silver to an ounce of water。 When nearly； but not quite； dry； dip it into a solution of twenty…five grains of iodide of potassium to one ounce of distilled water； drain it； wash it in distilled water and again drain it。 Now brush it over with aceto…nitrate of silver； made by dissolving fifty grains of nitrate of silver in one ounce of distilled water； to which is added one sixth of its volume of strong acetic acid。 Dry it with bibulous paper； and it is ready for receiving the image。 When the impression has been received； which will require from one to five minutes according to the state of the weather； it must be washed with a saturated solution of gallic acid to which a few drops of the aceto…nitrate of silver； made as above； have been added。 The image will thus be gradually brought out； and may be fixed with hyposulphite of soda。 To obtain the positive picture； paper must be used brushed over with an ammonio…nitrate of silver； made thus： forty grains of nitrate of silver is to be dissolved in one ounce of distilled water； and liquid ammonia cautiously added till it re…dissolves the precipitate。
A pleasing effect may be given to calotype； or indeed to all photographic pictures； by waxing them at the back； and mounting them on white paper； or if colored paper be used； various beautiful tones of color are produced。
POSITIVE CALOTYPE。
At a meeting of the British Association； Professor Grove described a process by which positive calotype pictures could be directly obtained； and thus the necessity to transfer by which the imperfections of the paper are shown； and which is moreover a troublesome and tedious process； is avoided。 As light favors most chemical actions； Mr。 Grove was led to believe that a paper darkened by the sun （which darkening is supposed to result from the precipitation of silver） might be bleached by using a solvent which would not attack the silver in the dark； but would do so in the light。 The plan found to be the most successful is as follows： ordinary calotype paper is darkened till it assumes a deep brown color； almost amounting to black； it is then redipped into the ordinary solution of iodide of potassium； and dried。 When required for use it is drawn over dilute nitric acid one part acid to two and a half parts water。 In this state； those parts exposed to the light are rapidly bleached； while the parts not exposed remain unchanged。 It is fixed by washing in water； and subsequently in hyposulphite of soda； or bromide of potassium。
Mr。 Grove also describes a process for converting a negative calotype into a positive one； which promises； when carried out； to be of great utility。
Let an ordinary calotype image or portrait be taken in the camera； and developed by gallic acid； then drawn over iodide of potassium and dilute nitric acid and exposed to full sunshine； while bleaching the dark parts； the light is redarkening the newly precipitated iodide in the lighter portions and thus the negative picture is converted into a positive one。
The calotype process has been applied to the art of printing； in England； but it possesses no advantages whatever over the method； with type； now so gloriously brought to perfection； and I can hardly think it will ever be made of any utility。 For the benefit of the curious； however； I will give Mr。 Talbot's method。
Some pages of letter…press are taken printed on one side only； and waxed； to render them more transparent； the letters are then cut out and sorted。 To compose a new page lines are ruled on a sheet of white paper； and the words are formed by fixing the seperate letters in their proper order。 The page being ready； a negative photograph is produced from it； from which the requisite number of positive photogenic copies may be obtained。
Another method； which requires the use of the camera； consists in employing large letters painted on rectangular pieces of wood； colored white。 These are arranged in lines on a tablet or board； by slipping them into grooves which keep them steady and upright； thus forming a page on an enlarged scale。 It is now placed before a camera； and a reduced image of it of the required size is thrown upon the sensitive paper。 The adjustments must be kept invariable； so that the consecutive pages may not vary from one another in the size of the type。 Mr。 Talbot has patented his process； but what benefit he expects to derive from it； I am at a loss to determine。
Enlarged copies of calotype or Daguerreotype portraits may be obtained by throwing magnified images of them； by means of lenses； upon calotype paper。
THE CHRYSOTYPE。
A modification of Mr。 Talbot's process； to which the name of Chrysotype was given by its discoverer； Sir John Herschel； was communicated in June 1843 to the Royal Society； by that distinguished philosopher。 This modification would appear to unite the simplicity of photography with all the distintness and clearness of calotype。 This preparation is as follows。
The paper is to be washed in a solution of ammonio…citrate of iron； it must then be dried； and subsequently brushed over with a solution of the ferro…sesquicyanuret of potassium。 This paper； when dried in a perfectly dark room； is ready for use in the same manner as if otherwise prepared； the image being subsequently brought out by any neutral solution of gold。 Such was the first declaration of his discovery； but he has since found that a neutral solution of silver is equally useful in bringing out the picture。 Photographic pictures taken on this paper are distinguished by a clearness of outline foreign to all other methods。
CHAP。 X。
CYANOTYPEENERGIATYPECHROMATYPEANTHOTYPEAMPHITYPE AND 〃CRAYON DAGUERREOTYPE。〃
The several processes enumerated at the head of this chapter； are all discoveries of English philosophers； with the exception of the third and last named。 Anthotype was first attempted by M。 Ponton a French savan； although it was reserved to Mr。 Hunt to bring the process to its present state。 The 〃Crayon Daguerreotype〃 is an improvement made by J。 A Whipple； Esq。； of Boston
I。 CYANOTYPE；
So called from the circumstance of cyanogen in its combinations with iron performing a leading part in the process。 It was discovered by Sir John Herschel。 The process is a simple one； and the resulting pictures are blue。
Brush the paper over with a solution of the ammonio…citrate of iron。 This solution should be sufficiently strong to resemble sherry wine in color。 Expose the paper in the usual way； and pass over it very sparingly and evenly a wash of the common yellow ferro…cyanate of potass。 As soon as the liquid is applied； the negative picture vanishes； and is replaced by a positive one； of a violet blue color； on a greenish yellow ground； which at a certain time possesses a high degree of sharpness； and singular beauty of tint。
A curious process was discovered by Sir John Herschel； by which dormant pictures are produced capable of developement by the breath； or by keeping in a moist atmosphere。 It is as follows。
If nitrate of silver； specific gravity 1。200 be added to ferro…tartaric acid； specific gravity 1。023； a precipitate falls； which is in a great measure redissolved by a gentle heat； leaving a black sediment； which； being cleared by subsidence； a liquid of a pale yellow color is obtained； in which the further addition of the nitrate causes no turbidness。 When the total quantity of the nitrated solution added amounts to about half the bulk of the ferro…tartaric acid； it is enough。 The liquid so prepared does not alter if kept in the dark。 Spread on paper； and exposed wet to the sunshine （partly shaded） for a few seconds； no impression seems to be made； but by degrees； although withdrawn from the action of light； it developes itself spontaneously； and at length becomes very intense。 But if the paper be thoroughly dried in the dark； （in which state it is of a very pale greenish yellow color；） it possesses the singular property of receiving a dormant or invisible picture； to produce which from thirty to sixty seconds' exposure to sunshine is requisite。 It should not be exposed too long； as not only is the ultimate effect less striking； but a picture begin