The Vreeland Spectroscope

The struggle to get spectra of burning calcium, magnesium and strontium with a Project Star™ spectroscope, convinced me that I would not be able to get spectra of the other two alkaline earths using that inexpensive instrument. As shown below, a piece of metal was clamped with tweezers and burned in front of the slit of the plastic spectroscope. When the metal ignited, a picture taken through the eyepiece:

Getting the metal to ignite, and thus emit the characteristic line spectra photons, was a challenge. It was necessary to use a blowpipe to initiate calcium which finally burned like magnesium only with an orange flame. Strontium usually melted before igniting and dripped onto the benchtop. When it did ignite it burned with a bright red flame and left smoke that smelled like roadside flares (which isn't surprising because strontium is used as the flame coloring agent in those flairs.) The sparkling flame left the spectrum seen here.

A major problem with this technique was spilled metal and metal oxides, so I attempted to suspend some burning strontium in a platinum basket to contain the molten metal and get a more controlable flame. That is not what happened:

The molten strontium ate a hole right through the platinum cage. Bummer. I think those things are about six hundred bucks. Platinum is usually quite stable to heat and corrosive environments. Dr. Ong hypothesized that the platinum and strontium formed a high temperature eutectic that melted through at a much lower temperature than the platinum would have melted.

Magnesium and berylluim are too refractory to get a spectrum by burning and barium requires a higher ignition temperature than can be obtained even using the blowpipe.

Enter the antique Vreeland carbon-arc visual spectroscope.

Magnesium acetate and barium carbonate placed on alumina (fire brick) boats provided easy access to the spectra of those elements. Using knobs (placed perilously close to the electrodes) a one by two centimeter boat containing a small scoop of the sample, was raised on a pedistal into an alternating current line voltage spark between two pencil sized carbon electrodes. The electrodes are easily replaced as they become contaminated with the sample and they slowly oxidize themselves. In fact the carbon electrodes impart a carbon emission pattern on all the spectra the Vreeland produces. You can still get a new Vreeland from Spectrex.

I had no beryllium salts in the laboratory, so I found it necessary to cut a sample from the marble sized piece of beryllium in the elements demonstration. I did not want to crush the ball, so I opted to 'bite' a piece off with metalworking tool. Donning gloves, a rubber apron, goggles and using the utmost care, I broke off a twenty five milligram sample which was placed into a weighing bottle.

The spectrum of beryllium did not jump right out, but appeared in a flickering spectrum after heating the sample in the spark for over a minute. You can see two characteristic blue beryllium lines flash in and out among the carbon lines in this one second animated loop of the spectrum.