Chemical retractions with caustic soda: 

Because The solution has a strong alkaline re­ac­tion, so litmus paper turns to dark blue (with phe­nolph­thalein the presence of the OH group gives a raspberry color, with methyl orange it may seem yellow). because of activity the substance, re­acts with almost any chemical compound

• Acids (it forms salts and water.)
• Am­pho­ter­ic hydroxides.
• Am­pho­ter­ic oxides (this re-action forms water and complex compound)
• Salts (caustic soda can provide the most of all effects of precipitation of metals, it forms a sediment in the form of metal hydroxides)
• Non-metal and halogens.
• Metals (apart from iron and copper, as they have a low elec­tro­chem­i­cal potential).
• Ethers and alkyl halides a hydrolysis re-­ac­tion arises.
• Poly­atom­ic alcohols (reagents may transform into alkox­ides)
• Fats (using for irreversible re­action of saponi­fi­ca­tion,in this process fats turn into soap and glycerin.)