THE WOMBAT. 59 



which the print is immersed in an acidified solution of hypo. 

 Acetic acid was generally used, but a similar result can be 

 •obtained by the addition of alum solution. When a gelatino- 

 •chloride print is placed in either mixture, it is first fixed, and, 

 if withdrawn at this stage and washed and dried, it has the 

 well-known red-brown colour of a print fixed in a neutral 

 "bath. If, however, it has been allowed to remain in the 

 liquid, it gradually would have acquired a colour that cannot 

 "be distinguished from the colour obtained by gold toning, 

 although of course no gold has been deposited. It follows 

 that the so-called "sulphur toning" is subsequent to, and 

 not simultaneous with fixing. Further, no difference was 

 observed between the effect of a hypo, solution that had been 

 acidified some time previously, and was very turbid with 

 precipitated sulphur, and a hypo, solution that had only 

 just been acidified and in which the precipitation of sulphur 

 was only just beginning. The addition of a lead salt, usually 

 in the form of acetate or nitrate, to the combined bath is 

 often recommended, mainly on the ground that it exerts an 

 influence on the molecular condition of the deposited gold, 

 .and yields prints of a more desirable colour than can be 

 obtained if the lead salts are omitted. If a solution con- 

 taining 20 parts of hypo, and one part of lead acetate per ioo 

 is used, the prints are first fixed, and subsequently acquire a 

 purplish colour indistinguishable from that obtained with a 

 gold bath, or with acidified hypo. Similar results are 

 obtained with lead nitrate in place of the acetate. Both 

 solutions are quite neutral in reaction, and do not pre- 

 cipitate sulphur, and hence although the resulting colour of 

 the print is similar to that obtained with acidified hypo, 

 it cannot be ascribed to the sulphur toning, and must be 

 brought about in a different way. The chief point to be 

 observed is, that in acidified hypo., or in hypo, containing a 

 lead salt, a gelatino-chloride print may acquire a colour that 

 cannot be distinguished from the colour obtained with gold. 

 Now it is generally admitted that the probable permanence of 

 a silver print is directly proportional to the quantity of gold 

 that has been deposited on the image. It is conceivable that 

 in a combined toning and fixing bath that contained or was 

 supposed to contain gold, and also had been mixed with alum 

 or a lead salt or both together, the actual toning or colour- 



R MONTEATH, 



RYRIE STREET, GEELONG. 



