Four prototype HALTT (" helicopter Alert and Threat Termination ") sensors are now on board Black Hawk helicopters and deployed to Afghanistan, as Danger Room alum Nathan Hodge reports.
四件HALTT(直升机预警与威胁解除)传感器样件目前已装在黑鹰直升机上，应用于阿富汗，如险情办公室Nathan Hodge所报道的。
In potash it turns black, but in alum nothing happens until you bring it to the boil, then purple colour comes flooding out.
在碳酸钾中，它变成黑色，而在明矾中一开始却什么反应都没有，直到煮沸后紫色都溢出来了。
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