say if you want to make 1000ml of 26.5%, you need 26.5x1000/90=294.4ml of 90% glycerol.

Yes, you are right! and add 705.6ml water.

Dear Sai babu Karimisetti

Dr. Guobing Xiang is very correct with the calculation.

You did your dilution calculation well but with poor accuracy. Small measuring cylinder can measure volume up to 0.1 ml accuracy, so try and be more careful.

You can simply measure the glycerol first and then make up the solution to 1000 ml; this would be more accurate because there may be changes in volume.

Regards.

Onyeka is right BUT You and Guobing are NOT.

Please, remember for your physical chemistry basic studies: volume is not an additive property.

BTW: are you sure that the glycerol content is volumetric %?

Laszlo is right, if you need to do it very accurately, use Onyeka's way: measure the glycerol first and then make up the solution to 1000 ml.

Thank you Dr. Laszlo Jicsinszky,

Although it's a good idea to always state explicitly the units used in percentages, but when not stated, certain conventions apply (% by convention, implies vol. % for concentrated liquid-liquid solution except for acid and base solution where wt. % applies; for very dilute solutions, w/v % applies)

Dear Sai babu Karimisetti,

You did not specify whether the concentration is vol. % or wt. %. but whichever unit you intend, just be consistent because the dilution formula demands consistency of units (C1V1=C2V2; if C is concentration on volume basis: vol. % or v/v or mol/v or g/v, then V must be volume, but if C is on mass basis: wt. % or wt/wt, then V must be taken as mass and in that case, you can either add 705.6 g of water to the concentrated solution as Dr. Guobing Xiang suggested or you add up to 1000 g solution. Though it sounds strange to be weighing liquids but it all depends on what you have; otherwise, use the density of the conc. solution (measure or obtain from your source of '90 %') and convert the conc. to vol basis in order to by-pass weighing of liquids.

If the unit is not known; perhaps you got the percentage value from the stock reagent bottle (and the unit was not explicit), simply follow the convention and work with volume as earlier stated.

My kind regards.