THE ALUMNI JOURNAL. 



24 r 



ments the correct method was estab- 

 lished. 



The metal portion of the cut is mount- 

 ed on a board of a thickness suited to the 

 particular frame used in the printing. 



It is inked with a fine ink, tempered 

 to the proper consistency with Calcutta 

 boiled oil and Japan drier. The precise 

 degree of temper depends on tempera- 

 ture, humidity, and other conditions. 



The inking is done by a simple hand 

 roller, of the kind used in ordinary 

 printing. 



The block lies face upward on the 

 table, and the piece of plain glass is 

 placed at the appropriate distance on a 

 level with it. A composition roller of 

 glue and molasses, made a trifle harder 

 than the regular printers' roller, is then 

 run forward on two guides. As it passes 

 over the block it takes the impression. 

 On reaching the glass, after one complete 

 revolution, it transfers the ink impression 

 directly to it. I do not think it possible 

 to run this roller evenly enough without 

 the steel guides ; at any rate, it would 

 not pay to waste time in trying it. 



The result is a print on the glass just 

 as if on paper. Curiously enough, the 

 prints on the glass are superior to those 

 on paper from the same block. The posi- 

 tives are then finished up as lantern slides 

 in the usual way. 



The superiority of the process lies in 

 its great cheapness. Ordinary slides 

 never cost less than fifty cents each. 

 Prepared in my way the first slide costs 

 about seventy-five eents, but the future 

 slides from the same block do not cost 

 over five cents each. 



The possibilities of the method are ex- 

 tensive. The publisher of an illustrated 

 book, for example, can print off sets of 

 slides for lecturers. Lectures on art, 

 botany, geology, history, etc., can be 

 provided at a small cost. Moreover, 

 views not taken from books could be 



prepared by first turning them into zinc 

 etchings, half-tones or woodcuts and then 

 printing from the blocks. The extensive 

 use of the lantern for purposes of instruc- 

 tion in the common schools is impracti- 

 cable at present, mainly owing to the 

 cost of the slides. With printed slides at 

 a trifling cost the difficulty is removed. 



People often complain that new ideas 

 may be useful, but that, when anyone 

 wants to put them in practice, it is diffi- 

 cult to find just the proper method. I 

 have given a description that makes the 

 method possible to every glass printer, 

 or to anyone willing to learn by practice. 

 Where such persons are not available, I 

 am willing to put anyone into communi- 

 cation with the printer of my own slides. 

 Scien tific A m erica n . 



American Peppermint Oil, — Power and Kle- 

 ber have made a very exhaustive examination 

 of pure oil of peppermint of American origin. 

 A large quantity was fractionally distilled. A 

 very small quantity came over between 3o°-i io°, 

 and consisted of acetaldehyde and isovaleric 

 aldehyde. A fairly large fraction, I55°-I70°, 

 consisted chiefly of pinene, but menthene could 

 not be detected. From 170 phellandrene was 

 obtained, and from I74°-I77° cineol was ob- 

 tained, and a tetrabromide, which was identi- 

 fied as that of limonene, was formed on treating 

 a higher fraction. The fraction from 205°-209° 

 gave menthone, and that from 209°-22o° con- 

 sisted of menthol. Under a pressure of 758 mm. 

 this boiled at 2 15. 5 . The higher boiling frac- 

 tions contained menthol ester. After this was 

 saponified menthol, and an oil distilling at 270 - 

 280 were obtained, which was found to be can- 

 dinene. The acid portion of the menthol ester 

 freed by means of sulphuric acid and distilled 

 with steam. Part was by this means trans- 

 ferred into a lactone. This had the composition 

 C 10 H 10 O2, and is not soluble in water, but 

 fairly so in most organic solvents. The hydroxy- 

 acid prepared from it, C 10 H 18 O 8 , crystallized in 

 needles, melting at 9.30. Acetic and isovaleri- 

 anic acids were also recognized in the products 

 of saponification. The remainder of the paper 

 deals with the method of estimating the men- 

 thol present by an acetylation method. — Be- 

 richte. 



