Record. xxv 



bones of the early bison in the glacial detritus through which 

 a storm sewer is being excavated at Tower Grove. 



A paper by Dr. T. Kodis, On the action of the constant 

 current upon animal tissue, was presented by the Secretary 

 and read by title. 



Professor F. E. Nipher stated that he wished to take this 

 occasion to correct some misapprehensions concerning the 

 development of photographic positives. He stated that the 

 effect of development in the light was to make the normal 

 exposure for positives shorter than when they are developed 

 in the dark-room. When for a given illumination of the 

 developing room the exposure has been properly made, the 

 ordinary developer used for negatives may also be used for 

 positives, without any restrainer. The restrainer is only 

 needed when the plate to be developed as a positive has been 

 under-exposed, or the plate to be developed as a negative 

 has been over-exposed. In both cases it is an approach to 

 the zero condition which calls for the restrainer. 



Professor Nipher added that Mr. Cockayne, of the Helio- 

 type Company, of Boston, had suggested to him the use of 

 potassium f erro-cyanide in place of potassium bromide in devel- 

 oping positives, and he had found it to give great brilliancy to 

 the pictures. A Cramer " Crown " plate exposed in a printing 

 frame for a couple of minutes at a south window, just out of 

 the direct rays of the sun, under a thin negative or positive, 

 may be developed at the same place. A few drops of ten 

 per cent, solution of the ferro-cyanide may be added, and 

 even as much as one part in twelve of developer has yielded 

 excellent results. The bath has in some cases been wholly 

 made up of the ferro-cyanide solution, the other chemicals 

 being added in dry form. The action of the ferro-cyanide is 

 quite different from that of bromide in equal strength, 

 although it may be largely a matter of degree. 



This bath should not be quite so strongly alkaline as for 

 negatives, in order to get the best results. The best results 

 when positives are developed in daylight are as fine as can be 

 obtained in the dark-room in the ordinary developing of nega- 

 tives. Various developers have been tried, but none of them 

 have yielded as good results as hydrochinon. 



