Magnesium Cyanide, Mg(CN)₂

Scheele treated magnesium hydroxide with hydrocyanic acid, and Schulz heated the double ferrocyanide of potassium and magnesium to redness, treated with water and evaporated, to obtain Mg(CN)₂. It is perhaps produced, in small quantities and very easily decomposed by moisture, by the action of carbon monoxide on heated magnesium.

The colourless solution of magnesium in hydrocyanic acid soon goes brown, and Mg(CN)₂ is so soluble and so easily hydrolysed that Schulz's "crystals" were probably magnesium hydroxide. Magnesium cyanide is also very soluble in alcohol.

When magnesium ferrocyanide is heated, the reaction

Mg₂[Fe(CN)₆] = 2Mg(CN)₂+FeC₂+N₂

occurs at about 200° C. At 400° C. only 3.30 per cent, of the cyanide is produced, and none at 800° C. - magnesium nitride resulting in greater and greater proportion as the temperature rises.

[Mg(OH)₂]+2HCN.Aq. = Mg(CN)₂.Aq. + 112.000 Cal.