SCIENTIEIC SUMMAKT. 
217 
A new method of Assaying Lead Oresbas been devised, according to tbe 
Chemical News ” [JFeb. 7, 1873], by Herr A. Mascazzini. Previous to re- 
ducing the galena or other lead ore to the metallic state, the author converts 
the lead present in the ore into sulphate by igniting it in a porcelain cruci- 
ble with sulphate of ammonia, after which the ore is treated in the usual 
manner. The flux preferred by the author is that recommended by Platt- 
ner, consisting of 13 parts of carbonate of potassa, 10 of dry carbonate of 
soda, 5 of previously fused borax, and 5 of well dried starch. 
MICROSCOPY. 
The microscopic characters of Cotton. — This subject has been frequently 
i attempted before. However, we think that the little pamphlet which the 
j Rev. H. Higgins, M.A., has sent us, is likely to^be better than most others. 
I It is illustrated by a number of photographs of the cotton of different 
kinds as seen beneath the microscope. Some of them are excellent. But 
j we confess that others appear as though they were photographed from 
i drawings. 
‘ Value of Chloride of Gold in Microscopy, — Dr. Woodward, of America, 
I thus expressed himself recently on this subject: — Attention was first drawn 
i to this reagent by the now renowned Dr. J. Cohnheim, in a paper on the 
I ending of the sensitive nerves of the cornea, published in Virchow’s 
' Archiv.” vol. xxxviii. p. 343, March 1867. It is true. Dr. Lionel S. Beale, 
the following year, informed his readers, in the fourth edition of How to 
Work with the Microscope,” that ‘‘ Cohnheim’s drawings alone ” excited 
doubts in his mind “ as to the accuracy of his observations ; ” and that 
I his statements should be received with the utmost caution.” Neverthe- 
I less, Cohnheim’s observations on the cornea have been substantially con- 
I firmed by numerous reliable observers, and the value of chloride of gold as 
I a histological reagent has become too well established for any authority, 
i however great, to sneer it away. 
i A new form of Mount for Microscopic objectives is described by Dr. R. L. 
j Maddox, in the “ Monthly MicroscopicalJournal ” for January. He says that 
i to others who, like himself, occasionally do a little glass grinding, the follow- 
ing form of mount may prove useful. It was made about two years ago. It 
; consists of the usual outer tube, but near the shoulder, on the outside, are 
turned a few threads of a coarse or fine screw, as desired, on which works 
the fine adjustment collar ; a slot, below or in front of the threads, permits 
a steel pin, which screws into the inner core or tube, to slide up and down, 
I according as the collar is rotated, the inner tube being carried up by a 
couple of turns of steel wire forming a spring, which works in a small space 
near the neck of the mount, bearing against a shoulder in front and above, 
against a stop attached to the top of the inner or core tube, which carries, as 
usual, the back and middle cells. It works quickly, easily ; has a con- 
siderable range, and no sensible slip ] moreover, its construction is not 
I difficult. 
The calcareous parts of the sucldng feet of Echinus. — This subject has been 
well illustrated in a paper accompanied by a plate in the “ Monthly Microsco- 
