The formulæ for the solution given by Whittaker, Laudy, and Parsons
are practically identical so far as the proportions of citrate of iron
and ammonia and of red prussiate of potash, 3 of the former to 2 of
the latter, but differ in the amount of water. Laudy's formula calls
for about 5 parts of water to 1 of the salts, Whittaker's for 4 parts,
and Parson's for a little more than 2 parts. The stronger the solution
the longer the exposure required. With very strong solutions a large
portion of the Prussian blue formed comes off in the washwater, and
when printing from glass negatives the fine lines and lighter tints
are apt to suffer. The blue color, however, will be deep and the
whites clear. With weak solutions the blues will be fainter and the
whites bluish. Heavily sized paper gives the best results. The
addition of a little mucilage to the solution is sometimes an
advantage, producing the same results as strength of solution, by
increasing the amount adhering to the paper. With paper deficient in
sizing the mucilage also makes the whites clearer.--_H.S.M., Sch. of
M. Quarterly._

* * * * *




HOUSE DRAINAGE AND REFUSE.


A course of lectures on sanitary engineering has been delivered during
the past few weeks before the officers of the Royal Engineers
stationed at Chatham, by Captain Douglas Galton, C.B., D.C.L., F.R.S.