Mr. R. Crossley on Algerite, a new Mineral Species. 1 79 



quarto page, and allow the paper to dry in the dark ; it is now 

 ready for the camera. While applying the sensitive coat, as 

 also while bringing out the picture, I take the precaution to 

 use a yellow light. I find that from ten to fifteen seconds is, 

 with ordinary sun-light, sufficient exposure, the latter being 

 generally too great. 



When the picture has been taken no trace of it appears on 

 the paper, but it comes speedily out on the application of a 

 saturated solution of gallic acid. I turn up the edges of 

 my paper and pour the solution on till the paper is entirely 

 covered, and keep it so till the picture has come sufficiently 

 out, when I fix it in the usual way. 



I find that if bromide of potassium be substituted for iodide 

 of potassium, in the first process, a picture is obtained; but 

 the time of exposure required is then about a minute. Again, 

 bromide or chloride of potassium does not serve to accelerate, 

 as in the ordinary processes, but the contrary; gallic acid too, 

 added to the aceto-nitrate, destroys sensitiveness. I find also, 

 that if the albumen be dried, and afterwards dissolved up 

 and used as above described, it has lost its photographic 

 value; a circumstance, which would seem to indicate that 

 photographic properties are connected with or dependent 

 Upon molecular arrangement. 



The employment of albumen in photography is not, I be- 

 lieve, new : it has not, however, so far as I am aware, been 

 used in the way or with the effect stated above. 

 Agra, 18th June, 1850. 



XXII. Algerite, a new Mineral Species. 

 By Richard Crossley, Esq.* 



A DETAILED description of this mineral by Mr. F. 

 Alger, accompanied with an analysis by Mr. T. S. Hunt, 

 was published in the American Journal of Science for July 

 1849, vol. viii. I have since, at the request of Mr. Alger, 

 made a re-examination. The results obtained vary but little 

 from those of Mr. Hunt, though this variation is essential to 

 the formula. Algerite, named by Mr. Hunt in honour of its 

 discoverer, Mr. Alger, is found in the town of Franklin, 

 Sussex County, New Jersey. It is sparingly disseminated in 

 prismatic crystals through a bed of pure crystalline limestone. 

 The crystals when undecomposed are of a honey-yellow colour, 

 and more or less penetrated by the matrix : some are conta- 

 minated by graphite, and others are encrusted with idocrase, 



* Communicated by W. G. Lettsom, Esq. 



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