Arsenic Element Number 33 As 

Arsenic is a gray metalloid with allotropes, The gray allotrope is a brittle crystalline form, with dull gray appearance.  Arsenic has a few important uses, other than being  a well known poison. The toxic nature has been used to murder, and kill people and pests as well.  A movie "Arsenic and old lace" starring Carey Grant, tells a story around Arsenic's poisonous quality.

The minerals orpiment and realgar are well known sources of Arsenic. Both were valued as medicine in the  Roman Empire, and as a yellow pigment for paints in China and the west. Realgar is a red crystal mineral used in red paints, both were used in fireworks.

 Arsenic  is used in farming as a food additive for animals specifically chickens, and pork. Arsenic  is still used in industrial insecticides, but less toxic than the As compounds used before. Arsenic  is a effective bacteria and fungicide.

Wood treatments in the US  with a compound of As, CCA, this has been replaced, for common lumber. CCA is a health risk, Arsenic  can leach from the wood into soil, and burning this material is a serious hazard! Do Not Burn PT wood! even the new stuff.  Some people suspect  that homes built with PT materials can release harmful Arsenic vapors.

Arsenic alloys are useful in semi conductors, Gallium Arsenide is 2nd to silicon in the industry. Other uses of Arsenic can be optical material, metallurgy, weapons and defoliants, colorants, and medicines. Many Arsenic uses have been phased out because of the toxic nature of the element.

Arsenic is thought to be used by some bacteria in a lake in California to replace Phosphorous. This means that a life form can use Arsenic as a building block.

Arsenic is a toxin in some drinking water, it can leach into water from man made sources such as PT wood, and also natural mineral sources. Arsenic also can be found in some forms in fish, mushrooms and other foods. Arsenic is also considered a carcinogen. A lab fee of about 100$ can determine the levels of As and other toxins in your water.

 This disc is a poly crystalline disc of Gallium-Arsenide. This material is popular in semi conductor manufacture.

 Sealed jar contains a chunk of pure As "metal" or pure elemental As in crystalline form.

These pretty yellow orpiment crystals are toxic, as they have a high percentage of Arsenic. This material was once used as yellow pigment in China. 

As 33 metalloid  AW: 74.9216  D:5.7  Sublimation: 1137   Mohs:3.5

Selenium Element Number 34 Se

 This pure Selenium disc has a soft feel and a look almost like Silicon, or Germanium.

Se 34 metalloid AW:78.96  D: 4.81  MP: 430  BP: 1265  Mohs: 2.0 

 Selenium is a glassy element, with a nice gray black tone, It also can be a nice red allotrope. Selenium is a relatively scarce element that is generally a byproduct material from refining Cu.

Selenium is used for a few industrial  applications. The major use is in glass manufacture, as a red color additive, also used as a catalyst in vulcanization of rubber. Selenium is used for a few alloys, and in X ray crystallography.

In the good old days Selenium could be found in large rectifiers, (the ones with big plates) but these days its less costly to use silicon based materials .Selenium is used for photocopiers and photo related applications, but these applications  are also being phased out. Selenium is still used in surge protection.

Selenium is also used as a nutritional supplement. sometimes found with vitamin E. as a trace supplement Selenium is helpful in the body, but in large doses Selenium has toxic effects.

Selenium has a few isotopes, and 3 are fission products, one of these is Se79 and  has a half life of 327,000 years and can help with study of radio active waste "disposal" over long term. 

Selenium rectifier NOS! 

Red Selenium allotrope as powder