Rail conveyance of chemical commodities. (Another point of view.)

of sources for theso esscntinl mnterinls. An iiivestig?tion cnrqicd out by nr. BIills nnd mysclf piit u s in possession of mctliods of manufnctiiro nnd of dctnils conccrning tilo constitution of both Pinnrerdol nnd Pinncynnol, nnd the ivholo of tho supplics of thoso tivo compounds required 11s the photogrnphic nir services of tho ~ i l l i cs tliroughnut tho wnr wcrc produced (ns Scnaitol Grccn nnd Sciisitol Red) in the clicmicnl Inhorntory of tho University of Cnmbridgc. Tho production of tl~cso .substnnccs in this country nnd tlw fainilinrity gniiied by our technicnl chcmists in denlinp witli tlieni rcsiiltcd in wry 81thstnntinl progress being mnclo in pnnchromntic photogrnphy. Tho best conimcrcinl pnnchromntic plntcs prcriously nvnilnblc rcqiiircil nbout thrco times tho csposuro for red ns for blue light, but tlioso now nvnilnblo require less exposuro for red tlinn for bluc. I n conscqiieiico of this progress nnchroinntic plntcs wcro produced which c o i i d bo used in nir pliotogrnpliy with nn cxposuro t h r o ~ g h n spcctroscopicnlly pure red screen of only 0.01 of n wconcl. ”his fnct is of grcnt importniico in wnr ncrinl pliotogrnplig, but i t ~ 4 1 ccrtninly become of fnr grcntcr rnltic nosv thrit ncrinl photography is becoming csscntinl in survcying and topogrnphy. tnlrs niid of tlio property ciitrustcd to tlicIi!? It nust !x n d m i t t d thnt tlic cortymnies with their vnst !snericiico of goods in trniislt really aro tho only