| Open and Closed Test Tubes |
|
Utilizing open and closed glass tubes with a heat (flame) source can be with the traditional blowpipe, Bunsen burner or a propane torch. I have tried the blowpipe and found I had to be a contortionist to adeptly accomplish what the simple, convenient portable propane torch easily achieves.
The primary purpose of either the close or open tube testing is an aid in comprehending the results of plaster and charcoal tablet sublimate mineral/metal identification.
No detailed images are provided regarding the variety of reactions using the open and closed glass tubes, because providing meaningful images is too difficult. These following images are essentially to assist the student of this almost lost art get a few basics, thus, perhaps making it easier to initiate these types of assays/tests.
I purchase glass tubes in 2 to 3 foot lengths, with OD diameters of 3/16” to ¼”.
The glass cutter will make any length of tube desired. I prefer using a 4” to a maximum of 6” length.
10x
To get the powdered or chunks of mineral into the open tube I simply use a match stick.
Any conveniently sized piece of wood or plastic rod allows the mineral to be placed about a ½” from end of tube. To avoid possible contamination don’t use any metal rods to push the mineral into the tube.
With experimentation I’ve found that a open tube in a slightly elevated position with gentle heating will partially solidify the mineral edges and thus not be as apt to fall back out of tube as it is elevated.
Elevating the tube creates a smokestack environment, allowing the heat to rise through the open tube.
By gradually increasing the tube to as near vertical as possible without losing the heated mineral the smoke and sublimation can rapidly occur.
Depending upon the composition of the minerals subjected to this type of test – smoke and sublimates will be seen developing.
By reading the provided blowpipe information a better comprehension of test procedures and results will develop after a little practice.
Only a single test can be conducted in an open tube primarily because the glass usually cracks/breaks upon reapplication of heat. I have re-used the same tube for identical mineral source to enhance sublimates, but generally this is impractical.
Normally, blow-pipe books refer to closed tubes for conducting sublimation & odor tests with dry pulverized solid minerals. However, closed glass tubes can be for conducting a wide variety of wet chemical digestions.
There’s a wide variety of closed glass tube shapes, with varying width, length with flat or rounded bottoms.
I primarily use the 1st two tubes (left) for only for wet tests, whereas the remaining 4 are for both wet and dry applications.
To conduct dry closed tube tests with powdered mineral and flame I place a glass funnel in the tube, which allows the pulverized mineral to come to rest on bottom of tube without touching (contaminating) side walls.
Conducting dry tests with the torch flame almost always destroys the closed glass tube, so an ample supply is advisable.
Wet tests usually allow multiple usages as long as a thorough cleaning is conducted prior to re-use.
A larger than normal closed glass tube exposed to the torch flame that contains nitric acid and water digesting a lead/silver ore.
The orange-red fumes of nitrous oxide are readily apparent, which is why I employed this image. Closed tube tests do not lend themselves to photography because the sublimates or smoke is usually subtle.
Normally, these types of tests are conducted within a semi-enclosed area to limit the amount of wind that may cause the torch flame to be inconsistent.