. The Pharmaceutical era. per thick-ness or else modify the length of the draw-tube until theimage appears with satisfactory clearness. For determining the thickness of cover glasses a coverglass gauge is used, one form of which is shown in theillustration. (Fig. 20.) The cover glass having beenplaced in the central depression, the spindle projectingat the right is turned until the cover glass is held firm-ly by the two projecting points seen in the central de-pression. The index on the drum then gives the propertube length for that thickness of cover. When no means of measuring the cover glas
. The Pharmaceutical era. per thick-ness or else modify the length of the draw-tube until theimage appears with satisfactory clearness. For determining the thickness of cover glasses a coverglass gauge is used, one form of which is shown in theillustration. (Fig. 20.) The cover glass having beenplaced in the central depression, the spindle projectingat the right is turned until the cover glass is held firm-ly by the two projecting points seen in the central de-pression. The index on the drum then gives the propertube length for that thickness of cover. When no means of measuring the cover glass is athand the remedy is to first focus the object as sharplyas possible, and then gradually alter the tube lengthuntil the greatest distinctness is obtained. The tubeis lengthened for cover glasses thinner than the stand-ard, and shortened for thicker ones. Multiple Nose Piece.—It will be remembered that the nosepiece is the milled ring on the lower end of the bodyinto which the objective screws. With this simple form. Fig. 20.—Cover tiauge. of nose piece, when it is desired to use an objective ofhigher or lower power than the one attached, the lattermust be unscrewed and another screwed on, an oper-ation requiring considerable time. This necessity is ob-viated by the use of the multiple nose piece, the mostcommon and useful of which are the double and triple.(Figs. 21 and 22.) In this the objectives are screwedinto a revolving frame attached to the body, and when-ever a change of power is desired it is only necessaryto revolve the frame until the desired objective isbrought into place, the exact adjustment usually beingindicated by the click of the spring which holds the ob-jective in its proper position. 392 THE PHARMACEUTICAL ERA. [Marc-h 17, 1898. Condensing Lens or Bulls-Eye Condenser.—When the lightreflected from an opaqu-e object is insuflicieut to showits surface clearly, or -when the mirror does not affordsufficient illumination for that purpose, it is c
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Keywords: ., bookcentury1800, booksubjectdrugs, booksubjectpharmacy, bookyear1
