The judgment of the court was delivered by

DESAI, J. - The assessee, Messrs. Hind Engineering Co., is a firm carrying on business in an article known as rubber belting. The said article is marketed by it under two different trade names, namely, "Hind rubber belting" and "Cooper rubber belting". The article in question is a rubber coated belt used as an accessory in the machinery employed for transmission of power. The assessee sold the articles marketed under the aforesaid two trade names under two separate invoices each dated 30th September, 1966. The assessee thereafter made two applications, each dated 22nd/24th December, 1966, to the Commissioner of Sales Tax, under section 52(1)(e) of the Bombay Sales Tax Act. 1959 (hereinafter referred to as "the Act"), for determination of the question whether any tax was payable in respect of this said two sales and, if so, the rate at which it was payable. The contention of the assessee in the said proceedings was that the articles sold by it were "cotton fabrics" within the meaning of entry 15 of Schedule A to the Act and, as such, no tax was payable on the sales of the said articles. In support of its contention, the assessee furnished a true copy of the test certificate dated 19th November, 1966, issued by the Assistant Director (Chemical), National Test House, Ministry of Supplies and Technical Development, Government of India, Calcutta, and the letter dated 30th March, 1967, written by the Mercury Rubber Mills, New Delhi, who are the manufacturers of these rubber beltings. The assessee also relied upon certain previous decisions of the Deputy Commissioner of Sales Tax (Appeals), Gujarat State, in which two articles of identical nature marketed under different trade names were held to fall within the ambit of entry 15 of Schedule A to the Act.

The Deputy Commissioner of Sales Tax (Headquarters), Gujarat State, before whom the said applications came up for hearing, negatived the contention of the assessee by two separate orders each dated 19th December, 1967. The Deputy Commissioner, inter alia, held that in the process of manufacturing rubber beltings, rubber was actually super-imposed on canvas after the weaving process of canvas cloth was completed. There was, therefore, a change in the original form of canvas cloth which was turned into rubber cloth and, as such, canvas cloth not retain is character as cloth or a cotton fabric. In the opinion of the Deputy Commissioner, therefore, rubber belting was not an item which fell within the ambit of entry 15 of Schedule A to the Act. The Deputy Commissioner further held that rubber belting was in fact an essential and integral part of the machinery in which it was commonly used and, therefore, it was covered by entry 15(1) of Schedule C to the Act.

The assessee, being aggrieved by the determination aforesaid, preferred two separate appeals before the Gujarat Sales Tax Tribunal (hereinafter referred to as "the Tribunal"). Two questions were raised before the Tribunal in the said two appeals. The first question was as to whether the determination of the Deputy Commissioner that rubber beltings were not covered by entry 15 of Schedule A was correct. The second question was whether the Deputy Commissioner ought to have directed under section 52(2) of the Act that the determination shall not affect the liability of the assessee as respects any sales of rubbers beltings effected prior to the determination. Since common questions were involved in both the appeals, the Tribunal heard them together and disposed them of by its common judgment and order dated 31st August, 1968. The Tribunal confirmed the decision of the Deputy Commissioner as regards the first question. As regards the second question, the Tribunal took the view that it was not obligatory on the part of the Deputy Commissioner to give the benefit of section 52(2) of the Act of the assessee and that the matter was one which involved the exercise of discretion by the Deputy