172 Miscellanies, 



ened parts will be acted upon in a different manner from those which re- 

 tain their original color, and after such action they will probably be no 

 longer affected by the rays of the sun, or, at all events, will have no ten- 

 dency to assimilate by such exposure; and if they remain dissimilar, the 

 picture will continue distinct, and the great difficulty be overcome. 



The first trials of the inventor to destroy the susceptibility of the metal- 

 lic oxide were entirely abortive ; but he has at length succeeded to an 

 extent equal to his most sanguine expectations. The paper employed by 

 Mr. Talbot is superfine writing paper; this is dipped into a weak solution 

 of common salt, and dried with a towel till the salt is evenly distributed 

 over the surface : a solution of nitrate of silver, is then laid over one side 

 of the paper, and the whole is dried by the heat of the fire. It is how- 

 ever, necessary to ascertain by experiment the exact degree of strength 

 requisite in both the ingredients, for if the salt predominates, the sensi- 

 bility of the paper gradually diminishes, in proportion to this excess, till 

 the effect almost entirely disappears. 



In endeavoring to remedy this evil, Mr. Talbot discovered that a re- 

 newed application of the nitrate not only obviated the difficulty, but ren- 

 dered the preparation more sensitive than ever : and by a repetition of the 

 same process the mutability of the paper will increase to such a degree, 

 as to darken of itself without exposure to the light. This shows that 

 the attempt has been carried too far, and the object of the experimenta- 

 list must be to approach, without attaining this condition. Having pre- 

 pared the paper and taken the sketch, the next object is to render it per- 

 manent, by destroying the susceptibility of the ingredients for this purpose. 

 Mr. Talbot tried ammonia and several other re-agents with little success, 

 till the iodide of potassium, greatly diluted, gave the desired result; this 

 liquid, when applied to the dra\ving, produced an iodide of silver, a sub- 

 stance insensible to the action of light. This is the only method of pre- 

 serving the picture in its original tints, but it requires considerable nicety, 

 and an easier mode is sufficient for ordinary purposes. It consists in 

 immersing the picture in a strong solution of salt, wiping off the super- 

 fluous moisture, and drying it by the heat of the fire: on exposure to the 

 sun, the white parts become of a pale lilac, which is permanent and 

 immoveable. Numerous experiments have shown the inventor that the 

 depth of these tints depends on the strength of the solution of salt; he 

 also mentions that those prepared by iodide become a bright yellow under 

 the influence of heat, and regain their original color on cooling. Without 

 the application of one of these preservatives the image will disappear by 

 the action of the sun ; but if inclosed in a portfolio, will be in no danger 

 of alteration : this, -Mr. Talbot remarks, will render it extremely conve- 

 nient to the traveller, who may take a copy of any object he desires, and 

 apply the preservative at his leisure. In this respect Mr. Talbot's system 

 is greatly superior to that of M. Daguerre, since it would be scarcely pos- 



