Abstract: An instrument for measuring the density of a liquid is disclosed comprising a housing having a solution chamber, and a separate instrument chamber. The solution and instrument chambers are separated by an isolating means, a portion of which is flexible. A lever passes through the flexible portion of the isolating means and is supported by a pivot assembly. A float is attached to one end of the lever and is at least partially submerged in the liquid being measured. Variations in the density of the liquid causes the float to rise and fall, and consequently, the lever rotates about the pivot axis. Position sensing electronics contained within the instrument chamber sense the position of the lever which is indicative of the liquid density. The isolating means includes an isolating partition having an opening formed therein, and a diaphragm. The diaphragm is clamped to a raised collar surrounding the opening in the isolating partition by a clamping ring.