This periodic table summarises daily upper intake limits for various elements (data taken from a variety of sources). Of the elements highlighted, Thallium is the most toxic. However, some of these elements, like copper, are essential minerals for which there is also a recommended daily intake. Remember, the dose makes the poison.
Recently I blogged about a plaster model made by James Clerk Maxwell in 1874 to visualise a relationship between volume, energy, and entropy. Follow-up discussion touched on the topic of data sculpture more generally, and I thought that such tangible three-dimensional data visualisations deserved their own post. The image below, for example, is of a spiral periodic table designed by Sir William Crookes and constructed in 1898 by his assistant:
Similar transparent data sculptures are relatively easy to make. The wide availability of 3d printers also allows easy generation of data sculptures. Jeff Hemsley explains how to do this with network data using R:
This plaster model was made by the great James Clerk Maxwell in 1874 (the photograph was by taken by James Pickands II, 1942). This historic artefact is one of three copies, held in museums around the world, including the Cavendish and the Sloane Physics Laboratory at Yale.
The model shows the relationship between volume, energy, and entropy for a fictitious water-like substance, based on theoretical work by Josiah Willard Gibbs. The lines connect points of equal pressure and of equal temperature. Maxwell found the model a useful aid in his research. The model prefigured modern visualisation techniques – today we would use computer software to visualise such surfaces, like this:
Infrared (IR) spectroscopy exploits the quantum-theoretic fact that the stretching or bending of chemical bonds involves specific amounts of energy, which correspond to specific IR frequencies (lower, microwave, frequencies cause molecules as a whole to move; higher, UV, frequencies can actually break chemical bonds).
The technique of IR spectroscopy was pioneered by William Coblentz at Cornell University during 1903–1905 (using the apparatus shown above), and had become a standard technique of chemistry by the 1950s. Traditionally, a prism or diffraction grating splits infrared light into different frequencies, while a movable mirror bounces specific frequencies of infrared light through a sample, and a detector measures how much of that light is absorbed. Prisms for this purpose cannot be made of glass, which absorbs infrared light, but prisms made of sodium chloride and other salts have been used. Modern devices use Fourier transform techniques, which do not require a prism or diffraction grating.
The image below is the result of using modern IR spectroscopy equipment (like that above). The vertical axis in this plot measures how much infrared light gets through:
This IR spectrum (in the mid-IR range 2.5–17 μm) is for aniline, which has an NH2 group attached to a benzene ring (see molecular structure below). Some of the key absorbance peaks are marked; these correspond to stretching and bending of N–H, C–H, C–N, and C–C bonds. The set of visible peaks form a fingerprint, which immediately identifies the substance aniline. For unknown compounds, the IR spectrum provides valuable clues to any molecular detective trying to determine the structure. Thank you, William Coblentz!
The Bunsen burner was invented in 1855 by the German chemist Robert Bunsen at the University of Heidelberg, assisted by Peter Desaga, an instrument maker there. Bunsen wanted a device that could produce heat without light, unlike the gas flames used for lighting at the time.
Bunsen was particularly interested in using the burner to identify elements by the colour of the flame they produced (or, more precisely, to identify elements by their emission spectrum). The image above shows the flames produced by placing salts of lithium, sodium, potassium, and copper in the flame of a Bunsen burner, for example. The image below shows the corresponding emission spectra (from top to bottom: Li, Na, K, Cu).