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| Dragon's egg ： ウィキペディア英語版 |
Dragon's egg
Dragon's eggs are fireworks pyrotechnic stars which first burn for a period for a visual effect then explode with a loud report. Manufacture of this effect became controversial because of the heavy metals once used, particularly lead tetroxide (Pb3O4). Nowadays, however, bismuth trioxide or bismuth subcarbonate are commonly used as more environmentally friendly substitutes for lead compounds to achieve the effect, and its occurrence in fireworks displays has since become much more common.
Because of its chemical makeup, a shell or cake containing mainly dragon's eggs is often noticeably heavier than a similar device containing other effects.
==References==
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抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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