It's a logo of a Thin Test Tube. The beaker has a dark outline and is white in the middle. The beaker is small and has a liquid inside just past halfway.
This is a Experiment icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,900 icons, all in the same style and quality.