1 68 Laboratory Arts 



oxygen direct from the same cylinder being used to convert this 

 into a blowpipe flame ; the oxy-methylated spirit, where the spirit 

 is fed to a small lamp, across which the oxygen is projected in the 

 form of a jet ; and lastly, the oxy-generator and ether-saturator 

 arrangement, which has the merit of being a completely portable 

 generating plant for both gases. Of all these the most generally 

 selected is the oxy-coal gas arrangement with blow-through jet, 

 as requiring least attention, least plant, and giving satisfaction in 

 the hands of an amateur. For high-class apparatus projection the 

 oxy-hydrogen mixed jet arrangement is the best, as a higher 

 illumination is secured, but more gas is used, specially hard lines 

 are required, and the installation is larger, more complex, and 

 much more sensitive to small deficiencies of adjustment than the 

 former system. The use of a " regulator " is recommended with 

 compressed gases, as this allows the supply to be cut off at the 

 lantern, without danger of blowing the connecting tube off the 

 nipples. 



Other illuminants may be considered unsuitable for the 

 projection of apparatus. 



2. Condenser. The condenser used should never be less than 

 4" diameter, and the makers may be trusted to supply the correct 

 article in other respects. It should be readily accessible from the 

 front, and admit of apparatus being placed close up to its front 

 surface. 



3. Slide Carriers. Various slide carriers of excellent design 

 are upon the market, that particularly recommended being Beard's 

 patent " Eclipse " carrier, which may be worked from one side of 

 the lantern, a point deserving of consideration. 



4. Objective. This should be of the " compound achromatic " 

 type. No simple objective has yet given the author complete 

 satisfaction, good definition of slides being only one desideratum ; 

 the objective should as accurately and clearly define the gradu- 

 ations of a burette as it does line diagrams upon slides. 



Theoretically a single lens should perform this more satis- 

 factorily than a compound one, owing to the thickness of the object 

 projected, but this does not appear to be the case practically. For 

 vertical cell work and similar purposes a single lens is sufficiently 

 good, however. 



Beyond this, the objective should be mounted so that adjust- 

 ments are made by rack and pinion, and that horizontal and 

 vertical alignment do not vary and require readjustment. A 6" 

 objective will be found generally most suitable in schools. It must 

 be easily removable from the rest of the lantern, in order to 



