MOEDANT. A class of substances used in dyeing, their effect being to cause the dyeing material to combine with the fabric to which it is applied, so that it cannot be removed by simple washing, or any ordinary treatment. Mordants are in general metallic oxides which have an affinity for the organic matter of the stuff, and by combining with it, c,ause the particles of the dye to combine also, and form a species of triple compound. The mordant most likely to be useful in photography is bichromate of potass when reduced by light. This enters into powerful combination with lignin, and takes down with it any particles of carbon, or pigment, or colouring matter that are mixed with the bichromate. In this way textile fabiics may be printed by photography. , MoSER'S IMAGES. M. Ludwig Miser has described at different times in "Toggendorff's Annalen," a vaiiety of curious experiments in which images were obtained by contact and developed by vapours in a similar way to the images in the process of Daguerre. From
these experiments he has drawn certain conclusions, which are generally supposed to be erroneous. For an account of them the reader is referred to " Hunt's Researches on Light," page 248. Mr. Grove, and Professor Volpicelli have also obtained latent images capable of being developed by vapours, by means of contact aided by electricity. The account of these experiments will be found in the 2nd volume of " Photographic Notes," edited by the author. This subject is one of great interest, and no doubt intimately connected with photography ; it is however at present involved in so much obscurity, that we think it better to refer the reader to other sources of infor mation than to occupy space in this work with more than a brief notice of it.