that the plaintiff has applied in writing to the patentee or exclusive licensee for a' written acknowledgements to the effect of the declaration claimed and has furnished him with full particulars in writing of the process or article in question; and

that the patentee or licensee has refused or neglected to give such an acknowledgement.

(2)

The costs of all parties in a suit for a declaration brought by virtue of this section shall, unless for special reasons the court thinks fit to order otherwise, be paid by the plaintiff.

(3)

The validity of a claim of the specification of a patent shall not be called in question in a suit for a declaration brought by virtue of this section, and accordingly the making or refusal of such a declaration in the case of a patent shall not be deemed to imply that the patent is valid or invalid.

(4)

A suit for a declaration may be brought by virtue of this section at any time after the publication of grant of a patent, and references in this section to the patentee shall be construed accordingly.