Instruments, Reagents and
Methods of Testing

The Blowpipe and Its Use
Many of the chemical tests made on minerals are performed by aid of an instrument known as a blowpipe. The blowpipe consists essentially of a tapering tube ending in a small and symmetrical opening through which air can be forced in a thin stream at high pressure This current of air, when directed into a luminous flame, converts it into a small and very hot flame, by means of which many important tests can be made.

Common type of blowpipe. The air is forced from the lungs into the mouthpiece, c, which fits into the upper end of the tube and issues from the small opening at the other end. The tip of the blowpipe, b, is placed just within a flat flame which is rich in carbon, such as is obtained from a candle or ordinary illuminating gas. A convenient method of producing a blowpipe flame is to use illuminating gas in a Bunsen burner, in which an inner tube. The gas flame is ordinarily adjusted so that it measures about 1 inch in height ½ inch in breadth. The blowpipe is introduced into this flame. the resulting blowpipe flame should nonluminous, narrow, sharp – pointed and clean – cut. If illuminating gas is not available, a candle with a flat wick or even an ordinary candle can be used. The latter require, however, more skill in manipulation.

The Art of Blowpiping
It usually requires some practice before one can produce a steady and continuous blowpipe flame.

Many tests can be made by means of a flame produced by exhausting the supply of air in the lungs simply once. But frequently an operation takes a longer time than this would give, and the interruption necessary in order to fill the lungs afresh would materially interfere with the success of the experiment. Consequently it often becomes important to be able to maintain a steady stream of air from the blowpipe for a considerable time. This is accomplished by distending the cheeks so as to form a reservoir of air in passage from the mouth into the throat is closed by lifting the root in through the nose a steady stream of air is also being forced out be obtained. It requires, however, considerable practice to do this skillfully.

The Character of the Blowpipe Flame
The inner cone, c, which is light blue in color and the most distinct part of the flame, is composed of unburned gas mixed with air from the blowpipe. There is no combustion taking place in this part of the flame. Around this cone is a narrow pale – violet cone, b, which is almost invisible and in which the combustion does take place. Any gas that is used for the production of the flame will consist of some combination of carbon and hydrogen. These elements when the gas is burned are converted into their respective oxides. The hydrogen burns directly to water vapour, H₂O. The carbon burns first to its lower oxide, CO₂, carbon dioxide. The final products of the combustion will, therefore, be the gases H₂O and CO₂. In cone b, where combustion is taking place, there will necessarily be considerable amounts of the lower oxide of carbon, co. Surrounding cone b there will be an invisible cone , consisting of the final products of combustion, CO₂ and H₂O.