Microchemical identification methods are often not very sensitive - we use solutions of about 1 to 10 grams of the substance per litre - but only a minute quantity of such a solution is needed. As one drop equivalent to 30 mg is sufficient, the detection limit is 0.3 to 0.03 mg, in some cases even well below these values! These methods are still used today for quick screening tests of minerals and non-destructive tests or examinations for valuables and pictures. Usually a tiny splinter of the sample is placed on the slide, heated with a drop of acid and covered with a coverslip. Then a suitable reagent is placed on the sideline of the coverslip and the resulting crystals are examined . Since the shapes of crytals are most typical this method is highly selective and meaningful.
One can even examine extremely inert minerals. A splinter of the mineral is heated together with a suitable fusing agent before the blowpipe, using a small loop made of platinum wire. Since locally temperatures far above 1000 oC are achieved even resistant minerals react with the fusing agent. The bead is then dissolved on the slide and microchemically investigated.
If you are interested in applying mikrochemical methods, download the pdf-files (German version, pictures are downsampled):
Doc-files, ready for print, with all the pictures in high quality (80 x 60 mm / 300 DPI), plus all the pictures seperately in high resolution (2048 x 1535 pixel), stored on CD-ROM, you can order using the mail address given below (EUR 20,-, postage included; outside Europe EUR 25,-, postage included).