diff --git a/frontend/js/labs/organic.js b/frontend/js/labs/organic.js
index 22e4673..d215779 100644
--- a/frontend/js/labs/organic.js
+++ b/frontend/js/labs/organic.js
@@ -1437,10 +1437,16 @@ class OrganicSim {
     ctx.lineTo(x + w - 4, y);
     ctx.stroke();
 
-    // clip to tube for liquid
+    // clip to the tube interior (straight sides + rounded bottom) so the
+    // liquid never spills past the glass outline
+    const rBot = w/2 - 4;
     ctx.beginPath();
-    ctx.rect(x + 4, liqY, w - 8, liqH - 8);
-    ctx.arc(x + w/2, y + h - (w/2 - 4), w/2 - 4, 0, Math.PI);
+    ctx.moveTo(x + 4, liqY);
+    ctx.lineTo(x + 4, y + h - rBot);
+    ctx.arcTo(x + 4,     y + h, x + w/2,   y + h, rBot);
+    ctx.arcTo(x + w - 4, y + h, x + w - 4, y + h - rBot, rBot);
+    ctx.lineTo(x + w - 4, liqY);
+    ctx.closePath();
     ctx.clip();
 
     // base liquid (reagent color)