. The microscope and microscopical methods. Microscopes; 1896. CH. VII.,] SLIDES AND COVER-GLASSES. 145 y-j-jr mm. may be put in the same box. For example, if one takes TW mm. as a standard, covers varying j~|T mm. on each side may be put into the same box. In this case the box would contain covers of y'j'V, ir. toV and Tyo- mm. JL_4. Fig. 122. Zeiss Cover-Glass Meas- urer. With i/iis the knife edge jaws are opened by means of a /ever, and the cover inserted. J lie thickness may /hen be read off on /he face as the pointer indicates /he thickness in hundredths millimeter in /he outer circle and
. The microscope and microscopical methods. Microscopes; 1896. CH. VII.,] SLIDES AND COVER-GLASSES. 145 y-j-jr mm. may be put in the same box. For example, if one takes TW mm. as a standard, covers varying j~|T mm. on each side may be put into the same box. In this case the box would contain covers of y'j'V, ir. toV and Tyo- mm. JL_4. Fig. 122. Zeiss Cover-Glass Meas- urer. With i/iis the knife edge jaws are opened by means of a /ever, and the cover inserted. J lie thickness may /hen be read off on /he face as the pointer indicates /he thickness in hundredths millimeter in /he outer circle and in hundred/Its inch on /he ae& inner circle. § 227. Cleaning Mixtures for Glass.—The cleaning mixtures used for cleaning slides and cover-glasses are those commonly used in chem- ical laboratories : (A) Dichromate of Potash and Sulphuric Acid. Dichromate of potash ( K, Cr2 Ot ) - - - 200 grams. Water, distilled or ordinary - - - 1000 cc. Sulphuric acid (H2 S04) - 1000 cc. Dissolve the dichromate in the water by the aid of heat. Pour the solution into a bottle that has been warmed and surrounded by a wet towel. Add slowly and at intervals the sulphuric acid. It is safer to mix the ingredients in an agate-ware basin, and put into the bottle only after the mixture is cool. For making this mixture, ordinary water, commercial dichromate and strong commercial sulphuric acid should be used. It is not necessary to employ chemically pure materials. This is a very excellent cleaning mixture, and is practically odorless. It is exceedingly corrosive and must be kept in glass vessels. It may be used more than once, but when the color changes markedly from that seen in the fresh mixture it should be thrown away. (Bj Sulphuric and Nitric Acid I\Iixture. Nitric acid (H NO,) - 200 cc. Sulphuric acid (H, SOJ ----- 300 cc. The acids should be strong, but they need not be chemically pure. The two acids are mixed slowly, and kept in a glass-stoppered bottle. This is a more corrosive mixture
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