in other industries, also, and consequently little is known about it. It has been associated with headaches and nausea and should be used with care.

Lithtwn earbonate is partially soluble and when ingested may cause severe lesions in the bone marrow and symptoms similar to pernicious anemia and leukemia. It is usually not fatal.

Manganese dioxtde is more dangerous than is commonly thought. It can be absorbed through either: inhalation or ingestion, It is an irritant and may cause an over- growth of the connective tissues in the brain and degeneration of certain of the motor functions of the central nervous system. Inhaled MnO9 gives rise to a variety of difficulties including stammering speech, muscular discoordination, paralysis, and spastic gait. All may be permanent. Three months to two years exposure is sufficient to cause any or all of these,

Complete cures are rare, due to the brain damage involved, but the progress of the disease may be successfully halted.

Only massive doses of Molubdenwn compounde are toxic. Repeated small doses are apparently harmless, since these materials are readily excreted from the body.

Due to their scarcity, not much research has been done on Rare Earths, but it is known that ecertum, yttriwn,

lanthanum, praeseodymiwn, and neodyniwn all have some

toxic effects.

Most seleniwn compounde are poisonous, but seleniin diowide is one of the most dangerous. Even simple contact with the skin can cause serious burns. Acute poisoning is similar in its symptoms to those of arsenic.

All thalZium compounds are poisonous. As little as one gram of ingested thallium may be fatal. Thallium compounds are used as rat poisons and dipilatories. They are rare in studio ceramics and, considering the dangers involved, are best left alone.

Vanadiwn pentoxide is absorbed by inhalation. The human

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